Hyperthermostable β-galactosidase gene, enzyme encoded thereby, and process for production

ABSTRACT

An isolated SDS-resistant hyperthermostable β-galactosidase gene derived from Pyrococcus furiosus. Examples thereof include genes respectively shown in SEQ ID NO: 1 and SEQ ID NO: 2 and genes each hybridizable with the above gene shown in SEQ ID NO: 1. A method of cloning the hyperthermostable β-galactosidase gene in which each of the above genes or pacts thereof is used as a probe or primer. A process for producing a hyperthermostable β-galactosidase by culturing a transformant into which a plasmid containing each of the above gene has been introduced.

This application is a Rule 53(b) divisional application of Ser. No. 08/489.733 filed Jun. 14, 1995 now U.S. Pat. No. 5,744,345 which is a continuation-in-part of now abandoned application Ser. No. 08/175,533 filed Dec. 30, 1993, which is a continuation-in-part of now abandoned application Ser. No. 08/128,079 filed Sep. 29, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a β-galactosidase, including an SDS-resistant β-galactosidase, which has a hyperthermostability and is useful in the food industry and a process for producing the same.

The invention also relates to a gene coding for the hyperthermostable β-galactosidase and a genetic engineering process for producing the enzyme which is useful in the fields of, for example, food industry and saccharide engineering.

2. Description of Related Art

β-galactosidase, which is an enzyme capable of decomposing β-galactoside, has been discovered in animals, plants and microorganisms. It is known that this enzyme occurs particularly in bacteria such as Escherichia coli, Streptococcus lactis, Bacillus subtillis, Streptococcus thermophilus and Sulfolobus solfataricus. Such a β-galactosidase in applied to the production of low-lactose milk by taking advantage of its ability to hydrolyze lactose into galactose and glucose. It is also applied to the production of galactose or glucose from lactose contained in milk serum which is formed in a large amount in the processor producing cheese.

To apply a β-galactosidase to food processing, therefore, it has been demanded to develop an enzyme that can withstand its use at a high temperature from the viewpoint of preventing contamination with microorganisms during processing and from another viewpoint of elevating the solubility of lactose which serves as a substrate.

Further, in recent years, various sugar compound productions are conducted with the use of a β-galactosidase glycosyltransfer reaction Japanese Patent Laid-Open No. 25275/1994 and Japanese Patent Laid-Open 14774/1994!. Thus, the development of highly thermostable enzymes is desired.

For example, a β-galactosidase originating in Sulfolobus solfataricus see European Journal of Biochemistry, 187, 321-328 (1990)! is a thermophilic enzyme having an activity at a temperature of 90° C. However, its activity falls to about 50% after treating at 85° C. for 180 minutes.

It is described in, for example, European Journal of Biochemistry, 213, 305-312 (1993), that β-galactosidase derived from the hyperthermophilic bacterium Pyrococcus furiosus exhibits its activity at high temperatures, thereby ensuring a high thermostability.

The inventors have discovered a hyperthermostable β-galactosidase having a residual activity ratio of about 80% even after treatment at 90° C. for 120 minutes and succeeded in isolating three types of β-galactosidases European Patent Laid-Open No. 0592158A2!. These three types of β-galactosidases are all hyperthemostable, and one of them is a β-galactosidase having an extremely high stability and exhibits its activity even in the presence of 1% sodium dodecyl sulfate (SDS).

SUMMARY OF THE INVENTION

As mentioned above, a thermophilic and thermostable enzyme is demanded in food processing and sugar compound production conducted at high temperatures. Further, if an enzyme holds its activity even in the presence of SDS which is known as a powerful surfactant, its application range can be widened.

In order to solve these problems, the present invention provides a β-galactosidase having an improved thermophilicity and an excellent thermostability.

The present invention also provides a gene coding for β-galactosidase having an improved thermophilicity and an excellent thermostability and provides a process for producing the hyperthermostable β-galactosidase with the use of the gene.

A further object of the present invention is to isolate a gene encoding a β-galactosidase having an improved thermophilicity, an excellent thermostability and resistance to surfactants, and to an industrial process for producing a hyperthermostable β-galactosidase with the use of the above gene.

To sum up the present invention, the first invention relates to a hyperthermostable β-galactosidase characterized by having a residual activity of about 80% or above after having been treated at 90° C. for 120 minutes.

The second invention relates to a process for producing a hyperthermostable β-galactosidase characterized by cultivating a bacterium of the genus Pyrococcus and recovering the β-galactosidase from the culture.

The third invention relates to an isolated DNA encoding a hyperthermophilic β-galactosidase which has the amino acid sequence shown in SEQ. ID NO. 1 of the Sequence Listing.

The fourth invention relates to an isolated DNA encoding a hyperthermophilic β-galactosidase of the third invention, which has the DNA sequence shown in SEQ. ID NO. 2 of the Sequence Listing.

The fifth invention relates to an isolated DNA encoding a hyperthermophilic β-galactosidase and having a DNA sequence which hybridizes with a DNA sequence of the third invention or fourth invention under stringent conditions.

The sixth invention relates to a process for producing a hyperthermostable β-galactosidase which comprises:

(a) constructing a plasmid in which an isolated DNA encoding a hyperthermophilic β-galactosidase as claimed in any one of the third to fifth inventions is inserted;

(b) transforming an appropriate host organism with said plasmid; and

(c) cultivating the transformed host organism and recovering the hyperthermophilic β-galactosidase from the culture.

The seventh invention relates to an isolated SDS-resistant hyperthermophilic β-galactosidase gene derived from Pyrococcus furiosus.

The eighth invention relates to the gene according to the seventh invention, which encodes a portion having an amino acid sequence shown in SEQ ID NO. 3 or a part thereof and having a hyperthermophilic β-galactosidase enzyme activity.

The ninth invention relates to the gene according to the seventh invention, which has a nucleotide sequence shown in SEQ ID NO. 4.

The tenth invention relates to an SDS-resistant hyperthermophilic β-galactosidase gene, which is hybridizable with the gene according to the eighth invention.

The eleventh invention relates to a method of cloning a hyperthermophilic β-galactosidase gene, which comprises using a gene according to any of the eighth to tenth inventions or a part thereof as a probe or a primer.

The twelfth invention relates to a process for producing a hyperthermophilic β-galactosidase, which comprises culturing a transformant, into which a recombinant plasmid containing the hyperthermophilic β-galactosidase gene according to the seventh invention has been introduced, and harvesting a hyperthermostable β-galactosidase from the culture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationships between the activities of the enzymes of the present invention with the use of o-nitrophenyl-β-D-galactopyranoside as a substrate and temperature, wherein the ordinate refers to the absorbance at 410 nm of the enzymatic reaction product while the abscissa refers to temperature.

FIG. 2 is a graph showing the relationships between the activities of the enzymes of the present invention with the use of lactose as a substrate and temperature, wherein the ordinate refers to the relative activity while the abscissa refers to temperature.

FIG. 3 is a graph showing the relationships between the activities of the enzymes of the present invention and pH, wherein the ordinate refers to the absorbance at 410 nm of the enzymatic reaction product while the abscissa refers to pH.

FIG. 4 is a graph showing the thermostabilities of the enzymes of the present invention, wherein the ordinate refers to the residual activity ratio while the abscissa refers to treating time.

FIG. 5 is a graph showing the pH stabilities of the enzymes of the present invention, wherein the ordinate refers to the residual activity ratio while the abscissa refers to treating pH.

FIG. 6 shows a restriction enzyme map of plasmid pTGE-101.

FIG. 7 shows a restriction enzyme map of plasmid pTGH-301.

FIG. 8 shows a restriction enzyme map of plasmid pTGEH-401.

FIG. 9 shows a restriction enzyme map of one example of a hyperthermophilic β-galactosidase gene of the present invention.

FIG. 10 is a graph showing the thermostability of a hyperthermophilic β-galactosidase of the present invention.

FIG. 11 is a graph showing the optimum pH of a hyperthermophilic β-galactosidase of the present invention.

FIG. 12 is a graph showing the optimum temperature of a hyperthermophilic β-galactosidase of the present invention.

FIG. 13 is a graph showing the pH stability of a hyperthermophilic β-galactosidase of the present invention.

FIG. 14 shows a restriction enzyme cleavage map of the plasmid pTG2ES-105.

FIG. 15 shows a restriction enzyme cleavage map of one form of the hyperthermostable β-galactosidase gene of the invention.

FIG. 16 shows the thermostability of an enzyme.

FIG. 17 shows the optimum pH of an enzyme.

FIG. 18 shows the optimum temperature of an enzyme.

FIG. 19 shows the pH stability of an enzyme.

FIG. 20 shows the thermostability of an enzyme in the presence of a surfactant.

FIG. 21 shows part (first half) of a view comparing amino acid sequences of various β-galactosidases.

FIG. 22 shows part (latter half) of a view comparing amino acid sequences of various β-galactosidases.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The microorganism to be used in the present invention is not particularly restricted, so long as it produces a hyperthermostable β-galactosidase. For example, strains belonging to the genus Pyrococcus exemplified by Pyrococcus furiosus DSM 3638 and Pyrococcus woesei DSM 3773 are usable therefor. Such a strain is cultivated in an appropriate growth medium and then the hyperthermophilic β-galactosidase according to the present invention can be obtained from the cells and the culture.

Now, the present invention will be described by referring to the use of a strain of the genus Pyrococcus as an example.

To cultivate a bacterium of the genus Pyrococcus, a method usually employed for cultivating a hyperthermostable bacterium may be used. Any nutrient which can be utilized by the employed strain may be added to the medium. For example, starch is usable as a carbon source and trypton and peptone are usable as a nitrogen source. As other nutrients, yeast extract and the like can be used. The medium may contain metal salts such as magnesium salts, sodium salts or iron salts as a trace element. It is advantageous to use artificial seawater for the preparation of the medium, as done in the present invention. The medium is preferably a transparent one free from a solid sulfur element, since such a medium makes it easy to monitor the growth of the cells by measuring the optical density of the culture. The cultivation can be effected either stationarily or under stirring. Alternatively, an aeration culture see Japanese Patent Publication No. 503757/1992! or a dialysis culture see Appl. Env. Microbiol., 55, 2086-2088 (1992)! may be carried out. In general, the cultivation temperature is preferably around 95° C. Usually, a considerably large amount of the β-galactosidase is accumulated in the culture within about 16 hours. It is a matter of course that the cultivation conditions should be determined in such a manner as to achieve the maximum yield of the β-galactosidase depending on the selected strain and the composition of the medium.

A β-galactosidase of the present invention can be recovered by, for example, collecting the cells from the culture broth by centrifuging or filtering and then disrupting the cells. The cell disruption can be effected by, for example, ultrasonic disruption, bead disruption of lytic enzyme treatment. By using these techniques, the β-galactosidase according to the present invention can be extracted from the cells. The enzyme may be extracted by a method capable of giving the highest extraction effect depending on the selected bacterium and thus a crude enzyme solution is obtained. From the crude enzyme solution thus obtained, the β-galactosidase can be isolated by combining technique commonly employed for purifying enzymes, for example, salting out with ammonium sulfate, ion exchange chromatography, hydrophobic chromatography and gel filtration.

For example, a crude enzyme solution prepared from cultivated cells of Pyrococcus furiosus DSM 3638 is chromatographed with a DEAE Toyopearl M650 ion exchanger (mfd. by Tosoh Corporation) to thereby elute an active fraction. The active fraction thus obtained is poured into an HIC-Cartridge Column (mfd. by Bio-Rad) to thereby elute an active fraction. The active fraction thus eluted is poured into a Superose 12 Column (mfd. by Pharmacia) or a Hydroxyapatite column (mfd. by Bio-Rad Laboratories) to thereby elute an active fraction. Thus three types of hyperthermophilic β-galactosidase of thus invention (E-I-1, E-I-2 and E-II) can be obtained. The enzymochemical properties of these hyperthermostable β-galactosidases are as follows.

(1) Activity

Each of E-I-1, E-I-2 and E-II has an activity of hydrolyzing lactose into galactose and glucose. Further, each of E-I-1, E-I-2 and E-II has an activity of hydrolyzing o-nitrophenyl-β-D-galactopyranoside into o-nitrophenol and galactose.

(2) Method for Determining Enzymatic Activity

In the determination of enzymatic activity, the o-nitrophenyl-β-D-galactopyranoside-hydrolyzing activity of an enzyme can be determined by spectroscopically monitoring o-nitrophenol formed via the hydrolysis of o-nitrophenyl-β-D-galactopyranoside. Namely, 5 μl of the enzyme solution of the present invention is added to a 100 mM phosphate buffer solution (pH 7.3) containing 112 mM of 2-mercaptoethanol and 1 mM of magnesium chloride to thereby give a total volume of 199 μl. Then 1 μl of a dimethyl sulfoxide solution containing 0.4 M of o-nitrophenyl-β-D-galactopyranoside is added thereto. After effecting a reaction at 95° C. for 30 minutes, the reaction is stopped by adding 100 μl of 0.1 M sodium carbonate and the absorbance of the reaction mixture at 410 nm is measured to thereby determined the amount of the o-nitrophenol thus formed. One unit of the hyperthermophilic β-galactosidase of the present invention is expressed in an amount of the enzyme whereby the absorbance at 410 nm can be increased by 1.0 at 95° C. within 1 minute. Each enzyme, E-I-1, E-I-2 and E-II, has an activity of decomposing o-nitrophenyl-β-D-galactopyranoside at pH 7.3 at 95° C., as measured above.

Further, the enzymatic activity of an enzyme of the present invention can be determined also by measuring the activity of decomposing lactose. The activity of decomposing lactose is measured by determining the amount of glucose formed by the decomposition of the substrate, as will be described hereinbelow. 5 μl of the enzyme solution is added to 70 μl of a 100 mM phosphate buffer solution (pH 7.3) containing 4 mM of magnesium sulfate. Next, 25 μl of a 2% lactose solution is added thereto and the mixture is reacted at 95° C. for 30 minutes. After stopping the reaction by cooling with ice, the amount of the liberated glucose is determined by using a glucose measurement kit Glucose B-Test Wako (mfd. by Wako Pure Chemical Industries, Ltd.). Each enzyme of the present invention, E-I-1, E-I-2 and E-II, has an activity of decomposing lactose at pH 7.5 at 95° C.

(3) Optimum Temperature

The optimum temperatures of the enzymes of the present invention, E-I-1, E-I-2 and E-II, are measured. With the use of 9.13 mU of E-I-1, 17.25 mU of E-I-2 and 11.35 mU of E-II, the activities of decomposing o-nitrophenyl-β-D-galactopyranoside are determined in accordance with the method described in item (2) above.

FIG. 1 shows the relationships between the o-nitrophenyl-β-D-galactopyranoside-decomposing activities of the enzymes, E-I-1, E-I-2 and E-II, and temperature, wherein the ordinate represents the absorbance at 410 nm of o-nitrophenol formed by the enzymatic reaction while the abscissa represents temperature (°C.), o represents E-I-1, Δ represents E-I-2, and □ represents E-II.

As FIG. 1 shows, each of the enzymes, E-I-1, E-I-2 and E-II, is active over a wide range of temperature of from 50 to 100° C. at the measurement pH value (7.3). In particular, E-I-1 shows a maximum activity at 100° C. E-I-2 and E-II each show an optimum temperature within a range of from 85 to 95° C.

Next, the optimum temperatures of the enzymes of the present invention with the use of lactose as a substrate are examined by using 45.6 mU of E-I-1, 172.5 mU of E-I-2 and 113.56 mU of E-II. The measurement is effected in accordance with the method described in item (2) above by using a 100 mM glycine-NaoH buffer solution (pH 7.5). FIG. 2 shows the relationships between the lactose-decomposing activities of the enzymes, E-I-1, E-I-2 and E-II, and temperature, wherein the ordinate represents the relative lactose-decomposing activities of E-I-1, E-I-2 and E-II calculated by taking the lactose-decomposing activity of each enzyme at 100° C. as 100%, while the abscissa represents temperature (°C.). In FIG. 2, each symbol has the same meaning as defined in FIG. 1.

As FIG. 2 shows, E-I-1, among the enzymes of the present invention, shows a maximum activity within a temperature range of from 90 to 105° C., while E-I-2 and E-II each show a maximum activity within a temperature range of from 90 to 110° C.

The reactions are carried out in a water bath (from 40 to 90° C.) and in an oil bath (from 90 to 120° C.). In particular, the reactions at a temperature exceeding 100° C. with the use of lactose as a substrate are performed in a vial provided with a screw cap so as to prevent the reaction mixture from boiling.

The optimum temperatures of the enzymes of the present invention, E-I-1, E-I-2 and E-II, are as follows.

E-I-1: 80-100° C. (using o-nitrophenyl-β-D-galactopyranoside as a substrate). 90-105° C. (using lactose as a substrate).

E-I-2: 75-95° C. (using o-nitrophenyl-β-D-galactopyranoside as a substrate). 90-110° C. (using lactose as a substrate).

E-II: 75-95° C. (using o-nitrophenyl-β-D-galactopyranoside as a substrate). 90-110° C. (using lactose as a substrate).

(4) Optimum pH Value

The optimum pH values of the enzymes, E-I-1, E-I-2 and E-II, are measured. 9.13 mU of E-I-1, 17.25 mU of E-I-2 and 11.35 mU of E-II are used. The measurement is effected by measuring o-nitrophenyl-β-D-galactopyranoside-hydrolyzing activities in accordance with the method described in item (2) above with the use of McIlvaine's buffer solution (pH 3.0 to 8.0) and a 100 mM glycine--NaOH buffer solution (pH 8.0 to 10.0). FIG. 3 shows the relationships between the o-nitrophenyl-β-D-galactopyranoside hydrolyzing activities of the enzymes, E-I-1, E-I-2 and E-II, and pH, wherein the ordinate represents the absorbance at 410 nm of o-nitrophenol formed by the enzymatic reaction while the abscissa represents pH. In FIG. 3, each symbol has the same meaning as defined in FIG. 1. Unfilled symbols show the data obtained by using McIlvaine's buffer solution and filled symbols show the data obtained by using the glycine sodium buffer solution.

As FIG. 3 shows, E-I-1 is active within a pH range of from 3.0 to 10.0 and has a maximum activity within a pH range of from 5.6 to 6.6. E-I-2 is activity within a pH range of from 3.0 to 10.0 and shows a maximum activity within a pH range of from 6.0 to 7.0. E-II is active within a pH range of from 3.0 to 10.0 and shows a maximum activity within a pH range of from 6.0 to 7.0.

The optimum pH values of the enzymes of the present invention, E-I-1, E-I-2 and E-II, are as follows.

E-I-1: pH 5.6-6.6

E-I-2: pH 6.0-7.0.

E-II: pH 6.0-7.0.

(5)Thermostability

The thermostabilities of the enzymes, E-I-1, E-I-2 and E-II, are measured. 9.13 mU of E-I-1, 17.25 mU of E-I-2 and 11.35 mU of E-II are used. The measurement is effected by treating the enzymes in 199 μl of McIlvaine's buffer solution of pH 6.0 (in the case of E-I-1) or McIlvaine's buffer solution of pH 6.6 (in the cases of E-I-2 and E-II) at 90° C. for various periods of time and then determining the o-nitrophenyl-β-D-galactopyranoside-hydrolyzing activities in accordance with the method described in item (2) above. FIG. 4 shows the thermostabilities of the enzymes, E-I-1, E-I-2 and E-II, wherein the ordinate represents the residual activity ratio (%) calculated by taking the activity of each enzyme in an untreated state as 100%, while the abscissa represents the treating time (minutes). In FIG. 4, each symbol has the same meaning as defined in FIG. 1.

As FIG. 4 shows, E-I-I has its enzymatic activity at a level of about 80% even after having been treated at 90° C. for 120 minutes. E-I-2 has almost its complete enzymatic activity after having been treated at 90° C. for 120 minutes. In the case of E-II, the enzymatic activity is not lowered but rather elevated by about 20% by having been treated at 90° C. for 120 minutes.

The thermostabilities of the enzymes of the present invention, E-I-1, E-I-2, E-II, are as follows.

E-I-1: About 80% of the activity is observed after having been treated as pH 6.0 at 90° C. for 120 minutes. After having been treated for 5 hours, about 50% of the activity is observed.

E-I-2: The activity is not lowered but sustained after having been treated at pH 6.6 at 90° C. for 120 minutes. After having been treated for 5 hours, about 90% of the activity is observed.

E-II: The activity is not lowered but rather elevated to about 120% after having been treated at pH 6.6 at 90° C. for 120 minutes. After having been treated for 5 hours, about 110 to 120% of the activity is observed.

(6) pH Stability

The pH stabilities of the enzymes of the present invention are examined. 9.13 mU of E-I-1, 34.5 mU of E-I-2 and 22.7 mU of E-II are used. McIlvaine's buffer solution is used in a pH range of from 3.0 to 8.0 and a 100 mM glycine-NaOH buffer solution is used in a pH range of from 8.0 to 10.0 To these enzymes are added 9 μl portions of the above-mentioned buffer solutions so as to give a total volume of 10 μl in each case. After having been treated at 90° C. for 30 minutes, 199 μl of McIlvaine's buffer solution of pH 6.0 (in the case of E-I-1) or 199 μl of McIlvaine's buffer solution of pH 6.6 (in the cases of E-I-2 and E-II) is added to determine the activity. The activity is determined by measuring the o-nitrophenyl-β-D-galactopyranoside-hydrolyzing activity at pH 7.3 in accordance with the method described in item (2) above. FIG. 5 shows the thermostabilities of the enzymes, E-I-1, E-I-2 and E-II, wherein the ordinate represents the residual activity ratio (%) calculated by taking the activity of each enzyme in an untreated state as 100% while the abscissa represents the treating pH value. In FIG. 5, each symbol has the same meaning as defined in FIG. 3.

As FIG. 5 shows, the enzymes of the present invention, E-I-1, E-I-2 and E-II, each remains stable within a pH range of 5.0 to 10.0 at the measurement temperature (90° C.).

E-I-1: sustains its activity after having been treated within a pH range of from 5.0 to 10.0 at 90° C. for 30 minutes.

E-I-2: sustains its activity after having been treated within a pH range of from 5.0 to 10.0 at 90° C. for 30 minutes.

E-II: sustains its activity after having been treated within a pH range of from 5.0 to 10.0 at 90° C. for 30 minutes.

(7) Substrate Specificity

Substrate specificity of the above-mentioned enzymes is determined by using p-nitrophenol-derivatives as shown in Table 1 below. The method is conducted as follows. 1485 μl of 150 mM sodium citrate buffer (pH 5.0) containing the above-mentioned enzymes is added to a quartz cuvette for a spectrophotometer. 15 μl of 0.1M substrate solution shown in Table 1 is added to the buffer and mixed. Immediately, reaction was followed to completion at 405 nm on the spectrophotometer. As a blank test, 1485 μl of 150 mM sodium citrate buffer (pH 5.0) not containing enzyme was used, and the determination described above was performed. The reaction was performed at 90° C. One unit of enzyme activity was defined as that amount required to catalyze the formation of 1 μmol p-nitrophenol.

According to the method described above, 0.028 units of E-I-1, 0.022 units of E-I-2, and 0.016 units of E-II were used. Hydrolytic activity towards p-nitrophenyl-β-D-glucopyranoside (GlcpβNp), p-nitrophenyl-β-D-galactopyranoside (GalpβNp), p-nitrophenyl-β-D-mannopyranoside (ManpβNp), p-nitrophenyl-β-D-xylopyranoside (XylpβNp), p-nitrophenyl-β-D-fucopyranoside (FucpβNp), and p-nitrophenyl-α-D-galactopyranoside (GalpαNp), was determined.

Results are shown in Table 1. Table 1 shows the specific activity of the above-mentioned enzymes, E-I-1, E-I-2, and E-II, towards the above-described substrates and their relative activities at 90° C. and pH 5.0.

                  TABLE 1     ______________________________________     Specific activity of the β-galactosidases     E-I-1           E-I-2       E-II             Specific                     Relative                             Specific                                   Relative                                         Specific                                               Relative             activity                     activity                             activity                                   activity                                         activity                                               activity     Substrate             U/mg    %       U/mg  %     U/mg  %     ______________________________________     GlcpβNp             0.776   100     32.3  100   44.6  100     GalpβNp             0.694   89.4    12.3  38.1  19.4  43.6     ManpβNp             0       0       54.8  169.4 3.3   7.5     XylpβNp             0       0       4.2   13.1  5.4   12.0     FucpβNp             0       0       0     0     0     0     GalpαNp             0       0       0     0     0     0     ______________________________________

Suitable selection of an above-mentioned enzyme, E-I-1, E-I-2, or E-II, is capable of optimal reaction towards a target substrate.

A genetic engineering process for producing a hyperthermostable β-galactosidase according to the invention comprises:

(a) constructing a plasmid in which an isolated DNA encoding a hyperthermophilic β-galactosidase as claimed in any of the first invention to the third invention is inserted;

(b) transforming an appropriate host organism with the plasmid; and

(c) cultivating the transformed host organism and recovering the hyperthermostable β-galactosidase from the culture.

The hyperthermostable β-galactosidase gene which includes an isolated DNA encoding a hyperthermophilic β-galactosidase of this invention can be screened and obtained by the expression cloning method using cosmid vectors. Expression cloning is a method which can be used for cloning of the gene coding some enzymes without any information about the primary structure of the target enzyme. For example, a pullulanase gene of Pyrococcus furiosus (WO 92/02614) is cloned using the expression cloning method. However, the method cannot be applied to cloning every type of enzyme because when a plasmid vector is used for the method, a suitable restriction enzyme is needed. It must cleave the target gene into a small enough size to be inserted in a plasmid vector and not cleave the target gene inside. Furthermore, the method is complicated because it needs a number of clones.

Subsequently, the present inventors have attempted to isolate the β-galactosidase gene by screening β-galactosidase activities in a cosmid library constructed with Pyrococcus furiosus genomic DNA and the cosmid vectors in which larger DNA fragments (35-50 kbp) can be inserted than in plasmid vectors. By using cosmid vectors, dangers for cleaving the target gene encoding the enzyme by a restriction enzyme decrease and the numbers of clones necessary to test can be reduced. On the other hand, enzyme activity may not be detected because of low expression of the enzyme since the cosmid vectors have less copy numbers in host organisms than plasmid vectors.

The present inventors observed an extremely high thermostability of the target enzyme and combined a process of cultivating the transformants in the cosmid library individually with a process of preparing the lysates which contain only the thermostable proteins. The group of these lysates is named "cosmid protein library". By using the library for detection of the enzyme activity, detection sensitivity increases over when using colonies of the transformants and bad influences such as background by proteins from hosts or inhibition of enzyme activity can be eliminated.

The present inventors isolated several cosmid clones which show β-galactosidase activity by screening the cosmid protein library constructed with Pyrococcus furiosus genomic DNA. The inventors searched the cosmid protein library derived from Pyrococcus furiousus, and obtained one cosmid clone exhibiting a β-galactosidase activity, though weak, in the presence of 1% SDS. Furthermore, the present inventors isolated the gene encoding a hyperthermostable β-galactosidase from the DNA fragments inserted in the clones isolated above by making full use of various genetic engineering techniques, and determined the DNA sequence of the gene. Moreover, the present inventors succeeded in the expression of the hyperthermostable β-galactosidase with the use of the gene, thus completing the present invention.

By the way, the expression cloning method using cosmid vectors which is described here cannot always be applied to any thermostable enzyme. The result is determined by the property of the target gene. For example, the present inventors attempted to isolate the gene encoding a protease (α-glucosidase) of Pyrococcus furiosus Appl. Env. Microbiol. 56, 1992-1998 (1990); Journal of Bacteriology, 172, 3654-3660 (1990)!, but they were unable to isolate the gene.

The microorganism to be used in the present invention is not particularly restricted, so long as it can produce a hyperthermostable β-galactosidase gene. For example, strains belonging to the genus Pyrococcus, i.e., hyperthermostable bacteria, such as Pyrococcus furiosus DMS 3638 Pyrococcus woesei DMS 3773 are usable therefor. These strains are both available from Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH.

For example, a cosmid library of Pyrococcus furiosus gene can be prepared in the following manner. First, the genome of Pyrococcus furiosus 3638 is partially digested by using an appropriate restriction enzyme, for example, Sau 3AI (mfd. by Takara Shuzo Co., Ltd.). After fractionating according to the size of 35 to 50 kbp, each DNA fragment thus obtained is ligated with an appropriate cosmid vector, for example, Triple Helix Cosmid Vector (mfd. by Stratagene). The Pyrococcus furiosus genome DNA fragments are first packaged in λ-phage particles by the in vitro packaging method and then an appropriate Escherichia coli strain, for example, E. coli DH5αMCR (mfd. by BRL) is transformed with the obtained phage solution to thereby give the desired cosmid library. Then cosmid DNAs are prepared from several colonies of the transformant and the insertion of the genome DNA fragments of 35 to 50 kbp into the transformant is thus confirmed. In general, 300 to 700 colonies may be incubated.

After the completion of the incubation of each colony, the incubated cells are collected. The cells are processed to the cosmid protein libraries by treating at 100° C. for 10 minutes, sonicating, and treating at 100° C. for 10 minutes once more. Then the β-galactosidase activity in the lysates obtained is determined (optionally in the presence of 1% SDS), whereby colonies expressing a hyperthermostable β-galactosidase which remain stable after the above treatment can be screened. The β-galactosidase activity is determined by, for example, using o-nitrophenyl-β-D-galactopyranoside or lactose (mfd. by Nacalai Tesque) as a substrate at a reaction temperature of, for example, 95° C. Next, the fragment inserted into the cosmid DNA of transformants showing activity is analyzed.

Inserted fragments in the cosmid DNAs of seven active transformants, among 500 transformants prepared by the present inventors, contain an EcoRI fragment of about 2.2 kbp in common. Thus this common DNA fragment is prepared to examine its properties. For example, a cosmid DNA expressing the activity is completely digested with a restriction enzyme EcoRI (mfd. by Takara Shuzo Co., Ltd.) and electrophoresed on a gel to thereby purify the target EcoRI DNA fragment of about 2.2 Kbp. Then the obtained fragment is inserted into the EcoRI site of an appropriate vector, for example, pUC19 (mfd. by Takara Shuzo Co., Ltd.). Thus a plasmid holding the common DNA fragment, which has been named pTGE-101 by the present inventors, can be prepared.

By this plasmid pTGE-101, an appropriate Escherichia coli strain such as E. coli JM109 is transformed. Thus a transformant named Escherichia coli JM109/pTGE-101 by the present inventors can be obtained. After incubating this E. coli transformant, the cells are collected and the β-galactosidase activity of the protein expressed in the cells is determined. The activity can be determined in the following manner. Namely, the cells and disrupted cells, which have been either thermally treated at 100° C. for 10 minutes, twice or untreated, are used and the above-mentioned o-nitrophenyl-β-D-galactopyranoside is employed as a substrate to effect a reaction at 70° C. or 95° C., whereby the thermostability of the expressed protein can be examined.

As Table 2 below shows, a gene coding for a thermostable β-galactosidase, which is inactivated when treated at 100° C. for 10 minutes twice but exhibits its activity at a reaction temperature of 70° C., has been inserted into pTGE-101.

                  TABLE 2     ______________________________________     Thermal treatment Reaction temperature     (100° C., 10 minutes, twice)                       70° C.                                95° C.     ______________________________________     Treated           -        -     Untreated         +        -     ______________________________________

In Table 2, symbol (+) indicates the presence of β-galactosidase activity, while symbol (-) indicates the absence thereof.

FIG. 6 shows a restriction enzyme map of the plasmid pTGE-101 wherein a thick solid line represents the EcoRI DNA fragment of about 2.2 kbp inserted into the plasmid pUC19. This fragment codes for the thermostable β-galactosidase. This fragment further codes for a part of the target hyperthermostable β-galactosidase.

The above-mentioned EcoRI DNA fragment of about 2.2 kbp is labeled. By using the labeled DNA fragment thus obtained as a probe, DNA fragments, which have been obtained by completely digesting cosmids having a hyperthermostable β-galactosidase gene with a restriction enzyme Hind III (mfd. by Takara Shuzo Co., Ltd.) and separating by agarose gel electrophoresis, are subjected to Southern hybridization. Thus a Hind III DNA fragment (about 3.3 kbp) hybridized with the probe can be identified. Then this fragment is extracted from the agarose gel and inserted into the Hind III site of an appropriate vector, for example, pUC19. Thus a plasmid, named pTGH-301 by the present inventors, can be prepared. By transforming E. coli JM109 with this plasmid, a transformant, named Escherichia coli JM109/pTGH-301 by the present inventors, can be obtained. This transformant is incubated and after completion of the incubation the cells are collected. The β-galactosidase expressed in these cells remains stable after treating at 100° C. for 10 minutes twice. Thus the target hyperthermostable β-galactosidase has been expressed therein.

FIG. 7 shows a restriction enzyme map of the plasmid pTGH-301 wherein a thick solid line represents the Hind III DNA fragment of about 3.5 kbp inserted into the plasmid pUC19. This fragment contains a hyperthermostable β-galactosidase gene. This fragment also contains the EcoRI DNA fragment of about 2.2 kbp shown in FIG. 6.

A part of the DNA sequence coding for the hyperthermostable β-galactosidase which is contained in plasmid pTGH-301 is shown in SEQ ID NO. 2 of the Sequence Listing. SEQ ID NO. 1 of the Sequence Listing shows the amino acid sequence deduced from the DNA sequence shown in SEQ ID NO. 2. Namely, SEQ ID NO. 1 of the Sequence Listing is the amino acid sequence of the hyperthermostable β-galactosidase which is produced with the use of an isolated DNA encoding a hyperthermostable β-galactosidase of the present invention. The isolated DNA encoding a hyperthermostable β-galactosidase of the present invention is also provided as an isolated DNA which has a DNA sequence encoding the amino acid sequence shown in SEQ ID NO. 1 of the Sequence Listing consisting of any combinations of genetic codes selected from degenerate codons.

Namely, the DNA sequence shown in SEQ ID NO. 2 of the Sequence Listing is an example of the hyperthermostable β-galactosidase gene given in the present invention.

Moreover, the N-terminal amino acid sequence of the purified sample of the hyperthermostable β-galactosidase produced by Escherichia coli JM109/pTGH301 agreed with the N-terminal amino acid sequence of the amino acid sequence shown in SEQ ID NO. 1 of the Sequence Listing.

From this plasmid pTGH-301, a Hind III-EcoRI DNA fragment (about 1.0 kbp) free from the hyperthermostable β-galactosidase gene can be eliminated in the following manner.

Namely, from three types of DNA fragments obtained by digesting the plasmid pTGH-301 with EcoRI, only one of about 1.0 kbp is eliminated and ligation is effected, followed by transduction into E. coli JM109. Then the hyperthermostable β-galactosidase activities of the obtained colonies are determined and a plasmid is prepared from a colony showing an activity.

The plasmid is named pTGEH-401, while E. coli JM109 transformed by this plasmid is named Escherichia coli JM109/pTGEH-401, and is deposited at the National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology, Japan, under the accession number of FERM BP-4468.

FIG. 8 shows a restriction enzyme map of the plasmid pTGEH-401, wherein a thick solid line represents the DNA fragment inserted into the plasmid pUC19.

FIG. 9 shows a restriction enzyme map of a DNA fragment originating in Pyrococcus furiosus which has been inserted into the plasmid pTGEH-401. Namely, FIG. 9 shows the restriction enzyme map of one example of the hyperthermostable β-galactosidase gene obtained according to the present invention.

When a transformant constructed by transducing a recombinant plasmid containing a hyperthermostable β-galactosidase gene such as Escherichia coli JM109/pTGH-301 or Escherichia coli JM109/pTGEH-401 is incubated, the hyperthermostable β-galactosidase is accumulated in the culture. The hyperthermostable β-galactosidase can be purified from this culture by, for example, harvesting the cells, disrupting the cells by ultrasonication and treating the supernatant obtained by centrifuging with a combination of purification procedures such as gel filtration chromatography, ion exchange chromatography and hydrophobic chromatography.

When the hyperthermostable β-galactosidase is to be purified in the present invention, in particular, it is advantageous to thermally treat the cells either before or after the ultrasonication, since the contaminating proteins are denatured thereby and thus the purified can be easily carried out.

The hyperthermostable β-galactosidase obtained by expressing a gene of the present invention, for example, a gene integrated in the plasmid pTGH-301 has the following physicochemical properties.

(1) Activity and Substrate Specificity

It has an activity of hydrolyzing lactose into galactose and glucose. Further, it has an activity of hydrolyzing o-nitrophenyl-β-D-galactopyranoside into o-nitrophenol and galactose.

(2) Method for Determining Enzymatic Activity

(2)-a!

In the determination of enzymatic activity, the o-nitrophenyl-β-D-galactopyranoside-hydrolyzing activity of an enzyme can be determined by spectroscopically monitoring o-nitrophenol formed via the hydrolysis. Namely, 5 μl of the enzyme solution of the present invention is added to 199 μl of a 100 mM phosphate buffer solution (pH 7.3) containing 112 mM of 2-mercaptoethanol and 1 mM of magnesium chloride. Then 1 μl of a dimethyl sulfoxide solution containing 0.4 M of o-nitrophenyl-β-D-galactopyranoside is added thereto. After effecting a reaction at 95° C. for 30 minutes, the reaction is stopped by adding 100 μl of 0.1 M sodium carbonate and the absorbance of the reaction mixture at 410 nm is measured to thereby determine the amount of the o-nitrophenol thus formed. One unit of the hyperthermostable β-galactosidase obtained in accordance with the present invention is expressed in an amount of the enzyme whereby the absorbance at 410 nm can be increased by 1.0 at 95° C. within 1 minute. The enzyme obtained in the present invention has an activity of decomposing o-nitrophenyl-β-D-galactopyranoside at pH 7.3 at 95° C., as measured above.

(2)-b!

The o-nitrophenyl-β-D-galactopyranoside-hydrolyzing activity of the β-galactosidase also can be determined by the following method. The enzyme reaction was started by adding 15 μl of a dimethyl sulfoxide solution containing 1 M of o-nitrophenyl-β-D-galactopyranoside into 1485 μl of McIlvaine's buffer solution containing the enzyme which is in a quartz cuvette for a spectrophotometer to give a final concentration of o-nitrophenyl-β-D-galactopyranoside of 10 mM. Reaction was detected by monitoring change of absorbance at 410 nm versus time on the spectrophotometer. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using an absorbance coefficient determined previously. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol per minute. Protein determination of the enzyme protein was performed by the method of Lowry's.

(2)-c!

Further, the enzymatic activity of the enzyme obtained in the present invention can be determined also by measuring the activity of decomposing lactose. The activity of decomposing lactose is measured by determining the amount of glucose formed by the decomposition of the substrate, as will be described hereinbelow. 5 μl of the enzyme solution is added to 70 μl of a 100 mM glycine sodium buffer solution (pH 7.5) containing 4 mM of magnesium sulfate. Next, 25 μl of a 2% lactose solution is added thereto and the mixture is reacted at 95° C. for 30 minutes. After stopping the reaction by cooling with ice, the amount of the liberated glucose is determined by using a glucose measurement kit Glucose B-Test Wako (mfd. by Wako Pure Chemical Industries, Ltd.). The enzyme obtained in the present invention has an activity of decomposing lactose at pH 7.5 at 95° C.

(3) Thermostability

By using 32 mU of the enzyme obtained in the present invention, the thermostability of the enzyme is measured. The measurement is effected by determining the o-nitrophenyl-β-D-galactopyranoside-hydrolyzing activity of the enzyme in accordance with the method described in item (2) above except that the phosphate buffer solution is replaced by McIlvaine's buffer solution (pH 6.6) containing 112 mM of 2-mercapto-ethanol and 1 mM of MgCl₂. After treating the enzyme in 204 μl of the above-mentioned buffer solution at 90° C. for various periods of time, 1 μl of a dimethyl sulfoxide solution containing 0.4 M of o-nitrophenyl-β-D-galactopyranoside is added, followed by a reaction at 95° C. for 30 minutes. Then the reaction is stopped by adding 100 μl of 0.1 M sodium carbonate and the absorbance at 410 nm is measured to thereby determine the amount of the o-nitrophenol thus formed.

The enzyme obtained in the present invention exhibits a hyperthermostability and suffers from no decrease in enzymatic activity even after treating at 90° C. for 120 minutes.

The thermostability of the β-galactosidase was determined in accordance with the method described in (2)-b!. 1 ml of McIlvaine's buffer solution containing the enzyme (pH 5.0) was incubated at 90° C. and aliquots were withdrawn at appointed times. The enzyme reaction was started by adding 10 μl of the aliquot to 1490 μl of McIlvaine's buffer solution (pH 5.0) containing 10 mM of o-nitrophenyl-β-D-galactopyranoside which had been incubated at 90° C. in the cuvette. Reaction was detected by monitoring absorbance at 410 nm versus time with a spectrophotometer. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined previously. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol per minute.

As FIG. 10 shows, about 100% of the activity of the β-galactosidase was retained even after treating at 100° C. for 150 min. FIG. 10 is a graph showing the thermostability of β-galactosidase wherein the ordinate represents the residual activity ratio (%), while the abscissa represents the treating time (minutes) at 90° C.

(4) Optimum pH Value

The optimum pH value of the β-galactosidase was measured in accordance with the method described in (2)-b! above. 1490 μl of McIlvaine's buffer solution which was determined to have its appointed pH value (pH 4-8) and containing 10 mM of o-nitrophenyl-β-D-galactopyranoside was incubated at 90° C. in the cuvette and the enzyme reaction was started by adding 10 μl of McIlvaine's buffer solution (pH 5.0) containing the enzyme into the cuvette. Reaction was detected by monitoring the change of absorbance at 410 nm versus time with a spectrophotometer. Change of absorbance at 410 nm per minute was determined. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined at each pH condition. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol in a minute. As shown in FIG. 11, the β-galactosidase shows its maximum activity at a pH range of from 4.5 to 6.5. FIG. 11 is a graph showing the optimum pH value of the β-galactosidase wherein the ordinate represents the specific activity (units/mg protein), while the abscissa represents treating pH.

(5) Optimum Temperature

The optimum temperature of the β-galactosidase was measured in accordance with the method described in (2)-b!. 1485 μl of McIlvaine's buffer solution (pH 5.0) containing the β-galactosidase was incubated at the appointed temperature (45° C.-90° C.) in the cuvette and the enzyme reaction was started by adding 15 μl of a dimethyl sulfoxide solution containing 1 M of o-nitrophenyl-β-D-galactopyranoside to give the final concentration of n-nitrophenyl-β-D-galactopyranoside to 10 mM. Reaction was detected by monitoring change of absorbance at 410 nm versus time with a spectrophotometer. Change of absorbance at 410 nm per minute was determined. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined at each temperature. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol per minute. As FIG. 12 shows, the β-galactosidase shows its maximum activity above 90° C. FIG. 12 is a graph showing the optimum temperature of the β-galactosidase wherein the ordinate represents the specific activity (units/mg protein), while the abscissa represents treating temperature (° C.).

(6) pH Stability

The pH stability of the β-galactosidase is determined in accordance with the method described in (2)-b!. 1485 μl of McIlvaine's buffer solution containing 20 units/ml of the β-galactosidase was incubated at the appointed pH (pH 3-8) for 10 minutes at 90° C. To start the reaction, 10 μl of aliquot of the enzyme solution was added to 1490 μl of McIlvaine's buffer solution (pH 5.0) which contained 10 mM of o-nitrophenyl-β-D-galactopyranoside and was preincubated at 90° C.

Reaction was detected by monitoring the change of absorbance at 410 nm versus time with a spectrophotometer. Change of absorbance at 410 nm in a minute was determined. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined previously. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol in a minute. As FIG. 13 shows, the β-galactosidase sustains its activity even after treating within a pH range of from 4.5 to 8.0 at 90° C. for 10 minutes. FIG. 13 is a graph showing the optimum pH value of the β-galactosidase wherein the ordinate represents the residual activity ratio (%), while the abscissa represents treating pH.

(7) Substrate Specificity

Substrate specificity of the β-galactosidase can be determined by using p-nitrophenol derivatives as shown in Table 3 below. The method is conducted as follows. 1485 μl of 150 mM sodium citrate buffer solution (pH 5.0) containing the β-galactosidase is added to a quartz cuvette for a spectrophotometer. 15 μl of 0.1M substrate solution shown in Table 1 is added to the enzyme solution and mixed. Immediately, reaction was detected by monitoring the change of absorbance at 410 nm versus time with a spectrophotometer. As a blank test, 1485 μl of 150 mM sodium citrate buffer (pH 5.0) not containing enzyme was used, and the determination described above was performed. In the test, reaction was performed at 90° C. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol p-nitrophenol per minute.

According to the method described above, hydrolytic activity towards p-nitrophenyl-β-D-glucopyranoside (GlcpβNp), p-nitrophenyl-β-D-galactopyranoside (Galp6`Np), p-nitrophenyl-β-D-mannopyranoside (ManpβNp), p-nitrophenyl-β-D-xylopyranoside (XylpβNp), p-nitrophenyl-β-D-fucopyranoside (FucpβNp), and p-nitrophenyl-α-D-galactopyranoside (GalpαNp), was determined.

Results are shown in Table 3, which shows specific activity (units/mg protein) of the β-galactosidase towards the above-described substrates and relative activity (%).

                  TABLE 3     ______________________________________     Specific activity of the β-galactosidase                     Specific                             Relative                     activity                             activity     Substrate       U/mg    %     ______________________________________     GlcpβNp    79.2    100     GalpβNp    28.8    36.4     ManpβNp    131.2   165.7     XylpβNp    10.5    13.2     FucpβNp    0       0     GalpαNp   0       0     ______________________________________

Substrate specificity of the β-galactosidase was also determined by using the natural substrate as shown in Table 4 below. The method is conducted as follows. Each substrate as shown in Table 4 was dissolved in 2 ml of 150 mM sodium citrate buffer (pH 5.0) so as to give a final concentration equivalent to 17 g/l for carboxymethyl-cellulose, avicel, or laminarin, and to 50 mM for the other substrates. After incubating these solutions at 90° C., 5 μl of phosphate buffer (pH 5.0) containing the β-galactosidase was added and the reaction was performed at 90° C. for 5 minutes. After stopping the reaction by cooling with ice, the amount of the liberated glucose was determined by using a glucose measurement kit Glucose C-Test Wako (mfd. by Wako Pure Chemical Industries, Inc.) One unit of enzyme activity was defined as that amount required to catalyze the hydrolysis of 1 μmol of the substrate in a minute. Results are shown in Table 4.

                  TABLE 4     ______________________________________     Substrate specificity of the β-galactosidase                       Relative                       activity     Substrate         %     ______________________________________     Lactose           100     Cellobiose        209.3     β-methyl-D-glucoside                       6.5     Salicin           89.0     Arbutin           4.5     Sucrose           0     Maltose           0     Carboxymethyl-cellulose                       0     Avicel            0     Laminarin         0     ______________________________________

SDS-Resistant β-Galactosidase

The fragments inserted into the cosmid DNA of one transformant having exhibited an activity among 500 transformants prepared by the inventors are cleaved with the use of various restriction enzymes, and the resultant fragment group is inserted into a suitable vector. For example, the cosmid DNA prepared from the above-mentioned cosmid clone is digested with Hind III (manufactured by Takara Shuzo Co., Ltd.), and the obtained DNA fragments are inserted into the Hind III site of the plasmid vector pUC18 (manufactured by Takara Shuzo Co., Ltd.). Thus a recombinant plasmid can be obtained.

Subsequently, this recombinant plasmid is introduced into the Escherichia coli JM109 (manufactured by Takara Shuzo Co., Ltd.) to thereby obtain a transformant, which is cultured and harvested. The activity of the β-galactosidase, a protein expressed in the cells, is assayed. The assay is conducted with respect to the cells and lysate thereof having undergone heat treatment at 100° C. for 10 minutes twice by using o-nitrophenyl-β-D-galactopyranoside as a substrate in the presence of 1% SDS. The activity is assayed by conducting the reaction at 95° C. for 30 minutes.

The above transformant lysate has no activity recognized. Then, the activity search was conducted in the same manner with the use of each of the restriction enzymes Acc I, Bgl II, Eco RV, Pst I and Hinc II (all manufactured by Takara Shuzo Co., Ltd.), but no activity was found.

The same search was conducted with the use of restriction enzyme capable of providing longer DNA fragments than with the use of the above restriction enzymes, for example, Cla I (manufactured by Takara Shuzo Co., Ltd.). However, deletion was found in the insert fragments at the stage of insertion into the plasmid, and no activity was recognized. Next, the search was conducted in the same manner with the use of Sma I (manufactured by Takara Shuzo Co., Ltd.). As a result, activity was recognized in a plasmid having a DNA fragment of about 4 kbp inserted therein. This plasmid was designated plasmid pTG2S-112 by the inventors. By transforming Escherichia coli JM109 by this plasmid, a transformant designated as Escherichia coli JM109/pTG2S-112 by the present inventors can be obtained. This transformant is incubated and, after the completion of the incubation, the cells are collected. The β-galactosidase expressed in these cells remains stable irrespective of heat treating in the presence of 1% SDS at 100° C. for 10 minutes twice. Thus the target hyperthermostable β-galactosidase has been expressed therein.

Further, the plasmid pTG2S-112 is digested with various restriction enzymes, and the resultant fragments are inserted in suitable vectors. The resultant recombinant plasmids are introduced into Escherichia coli JM109, and the obtained transformants are cultured and harvested. The activity of β-galactosidase, a protein expressed in the cells, is assayed. Thus, a plasmid expressing hyperthermostable β-galactosidase can be searched for.

For example, the plasmid pTG2S-112 is digested with the restriction enzymes Eco81I (manufactured by Takara Shuzo Co., Ltd.) and Sma I. The resultant Eco81I-Sma I DNA fragment of about 2.0 kbp is purified and inserted in pUC18 to thereby obtain a recombinant plasmid.

Alternatively, with the utilization of the multicloning site of the vector (pUC18) region of pTG2S-112, ptG2S-112 is digested with the restriction enzymes Eco81I and Kpn I (manufactured by Takara Shuzo Co., Ltd.). The resultant Eco81I-Kpn I DNA fragment of about 4.7 kbp is purified, blunt-ended and self-ligated. Thus, a recombinant plasmid containing the above-mentioned Eco81I-Sma I DNA fragment of about 2.0 kbp can be obtained.

This plasmid is introduced into the Escherichia coli JM109, and the resultant colonies are assayed for the hyperthermostable β-galactosidase activities thereof. A plasmid is prepared from the colony having exhibited the activity. This plasmid is designated as plasmid pTG2ES-105. The Escherichia coli JM109 transformed with this plasmid is designated as Escherichia coli JM109/pTG2ES-105. This strain was deposited on Apr. 20, 1994 at the National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology (1-3, Higashi 1 Chome Tsukuba-shi Ibaraki-ken 305, JAPAN) under the accession number FERM BP-5023. A restriction enzyme cleavage map of the plasmid pTG2ES-105 is shown in FIG. 14, in which the thick solid line represents the fragment inserted in the plasmid pUC18.

FIG. 15 shows a restriction enzyme cleavage map of the DNA fragment derived from Pyrococcus furiosus and inserted in the plasmid pTG2ES-105. That is, FIG. 15 is a view showing the restriction enzyme cleavage map of the form of the hyperthermostable β-galactosidase gene obtained according to the present invention. The β-galactosidase expressed in the cells obtained by culturing the transformant designated as Escherichia coli JM 109/pTG2ES-105 followed by harvesting is stable irrrespective of the heat treatment conducted in the presence of 1% SDS at 100° C. for 10 minutes twice. Thus the target hyperthermostable β-galactosidase has been expressed therein.

The hyperthermostable β-galactosidase is accumulated by culturing a transformant, into which a recombinant plasmid containing the hyperthermostable β-galactosidase gene has been introduced, e.g., Escherichia coli JM109/pTG2S-112 or Escherichia coli JM109/pTG2ES-105. The purification of the hyperthermostable β-galactosidase from the culture may be effected, for example, by disrupting the harvested cells by sonication, centrifuging the lysate and subjecting the resultant supernatant to gel filtration chromatography, ion exchange chromatography, hydrophobic chromatography or the like.

When the hyperthermostable β-galactosidase is to be purified in the present invention, in particular, it is advantageous to thermally treat the cells either before or after the ultrasonication, since the contaminating proteins are denatured thereby and thus the purification can be easily carried out.

The hyperthermostable β-galactosidase obtained by expressing a gene of the present invention, for example, a gene integrated in the plasmid pTG2ES-105 has the following physicochemical properties.

(1) Activity

It has an activity of hydrolyzing lactose into galactose and glucose. Further, it has an activity of hydrolyzing o-nitrophenyl-β-D-galactopyranoside into o-nitrophenol and galactose.

Further, it has an activity of hydrolyzing o-nitrophenyl-β-D-galactopyranoside into o-nitrophenol and galactose under 50 mM phosphate buffer (pH 7.0) containing 1% SDS.

(2) Method for Determining Enzymatic Activity

(2)-a!

In the determination of enzymatic activity, the o-nitrophenyl-β-D-galactopyranoside hydrolyzing activity of an enzyme can be determined by spectroscopically monitoring o-nitrophenol formed via the hydrolysis. Namely, 5 μl of the enzyme solution of the present invention is added to 199 μl of a 100 mM phosphate buffer solution (pH 7.0) containing 112 mM 2-mercaptoethanol, 1 mM magnesium chloride and 1% SDS. Then 1 μl of a dimethyl sulfoxide solution containing 0.4 M o-nitrophenyl-β-D-galactopyranoside is added thereto. After effecting a reaction at 95° C. for 30 minutes, the reaction is stopped by adding 100 μl of 0.1 M sodium carbonate and the absorbance of the reaction mixture at 410 nm is measured to thereby determine the amount of the o-nitrophenol thus formed. One unit of the hyperthermostable β-galactosidase obtained according to the present invention is expressed in an amount of the enzyme whereby the absorbance at 410 nm can be increased by 1.0 at 95° C. within 1 minute. The enzyme obtained in the present invention has an activity of decomposing o-nitrophenyl-β-D-galactopyranoside at pH 7.0 at 95° C. in the presence of 1% SDS.

(2)-b!

The o-nitrophenyl-β-D-galactopyranoside hydrolyzing activity of the β-galactosidase also can be determined by the following method. The enzyme reaction was started by adding 15 μl of a dimethyl sulfoxide solution containing 1 M o-nitrophenyl-β-D-galactopyranoside into 1485 μl of McIlvaine buffer solution (pH 5.0) containing the enzyme which is in a quartz cuvette for a spectrophotometer to give a final concentration of o-nitrophenyl-β-D-galactopyranoside of 10 mM. Reaction was detected by monitoring the change of absorbance at 410 nm versus time on a spectrophotometer. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined previously. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol per minute.

The assay of enzymatic proteins was carried out by the use of a protein assay kit (manufactured by Bio-Rad Laboratories).

(3) Thermostability

The thermostability was measured according to the following procedure in conformity with the method described in (2)-b!. 1.5 ml of a McIlvaine buffer (pH 5.0) containing an enzyme is heated at 90° C. for a given period of time, and 1485 μl of the resultant solution is sampled therefrom. The sample is heated in a cuvette of a spectrophotometer at 90° C. for 5 minutes, and 15 μl of a dimethyl sulfoxide solution containing 1 M o-nitrophenyl-β-D-galactopyranoside is added thereto to initiate a reaction. This reaction may be traced by calculating a change in absorbance at 410 nm per minute and determining the amount of o-nitrophenol liberated per minute from a previously determined extinction coefficient of o-nitrophenol.

The enzyme of the present invention has a residual activity ratio of about 100% even after heat treatment at 90° C. for 180 minutes as shown in FIG. 16. That is, FIG. 16 shows the thermostability of the enzyme, in which the ordinate indicates the residual activity ratio (%) and the abscissa indicates the period of time (minutes) for which the enzyme is treated at 90° C.

(4) Optimum pH

The optimum pH was measured according to the method described in (2)-b!. 2990 μl of McIlvaine buffer solution, which had a pH at an appointed value (pH 4-8) and containing 10 mM o-nitrophenyl-β-D-galactopyranoside, was incubated at 90° C. in the cuvette and the enzyme reaction was started by adding 10 μl of McIlvaine buffer solution (pH 5.0) containing the enzyme (150 units/ml) into the cuvette. Reaction was detected by monitoring the change of absorbance at 410 nm versus time on a spectrophotometer. Change of absorbance at 410 nm per minute was determined. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined at each pH condition. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol in a minute.

As shown in FIG. 17, the enzyme of the present invention shows its maximum activity at a pH range of from 4.5 to 5.5. FIG. 17 is a graph showing the optimum pH of an enzyme wherein the ordinate represents the specific activity (units/mg protein), while the abscissa represents treating pH.

(5) Optimum Temperature

The optimum temperature was measured according to the method described in (2)-b!. 2990 μl of McIlvaine buffer solution (pH 5.0) containing 10 mM o-nitrophenyl-β-D-galactopyranoside was incubated at appointed temperature (45° C.-90° C.) in the cuvette and the enzyme reaction was started by adding 10 μl of the enzyme (150 units/ml). Reaction was detected by monitoring the change of absorbance at 410 nm versus time on a spectrophotometer. Change of absorbance at 410 nm per minute was determined. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined at each temperature. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol per minute.

As FIG. 18 shows, the enzyme of the present invention shows its maximum activity about 95° C. FIG. 18 is a graph showing the optimum temperature of an enzyme wherein the ordinate represents the specific activity (units/mg protein), while the abscissa represents treating temperature (° C.).

(6) pH Stability

The pH stability was measured according to the method described in (2)-b!. McIlvaine buffer solution (pH 3.0-8.0) containing 150 units/ml of the enzyme and glycine buffer solution (ph 8.0-11.0) containing 150 units/ml of the enzyme was incubated for 10 minutes at 90° C. To start the reaction, 10 μl of the enzyme solution was added to 2990 μl of McIlvaine buffer solution (pH 5.0) which contained 10 mM of o-nitrophenyl-β-D-galactopyranoside and preincubated at 90° C.

Reaction was detected by monitoring the change of absorbance at 410 nm versus time with a spectrophotometer. Change of absorbance at 410 nm in a minute was determined. Based on the change of absorbance at 410 nm per minute, o-nitrophenol released per minute was calculated by using the absorbance coefficient determined previously. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol o-nitrophenol in a minute.

As FIG. 19 shows, the enzyme of the present invention sustains its activity even after treating within a pH range of from 5.0 to 10.0 at 90° C. for 10 minutes. FIG. 19 is a graph showing the pH stability of the enzyme wherein the ordinate represents the residual activity ratio (%), while the abscissa represents treating pH.

(7) Influence of Various Surfactants

The thermostability of the enzyme in the presence of each of various surfactants was measured according to the following procedure in conformity with the method described in (2)-b!. Sodium dodecyl sulfate (SDS) (manufactured by Nacalai Tesque) was used as an anionic surfactant, hexadecyl trimethyl ammonium bromide (manufactured by Nacalai Tesque) as a cationic surfactant, polyoxyethylene (20) sorbitan monolaurate (manufactured by Wako Pure Chemical Industries, Ltd.) as a nonionic surfactant, and sodium cholate (manufactured by Nacalai Tesque) as a cholic surfactant.

In the reaction solution, the concentration of the above surfactant was adjusted to 1%. 1.5 ml of a 50 mM phosphate buffer (pH 7.0) containing an enzyme is heated at 90° C. for a given period of time, and 1485 μl of the resultant solution is sampled therefrom. The sample is heated in a cuvette of a spectrophotometer at 90° C. for 5 minutes, and 15 μl of a dimethyl sulfoxide solution containing 1 M o-nitrophenyl-β-D-galactopyranoside is added thereto to thereby initiate a reaction. This reaction may be traced by calculating a change in absorbance at 410 nm per minute and determining the amount of o-nitrophenol liberated per minute from a previously determined extinction coefficient of o-nitrophenol.

The enzyme of the present invention has a residual activity ratio of about 80% even after heat treatment at 90° C. for 120 minutes in the presence of any of the surfactants except hexadecyl trimethyl ammonium bromide, as shown in FIG. 20. In particular, the enzyme of the present invention has a residual activity ratio of about 90% even after heat treatment at 90° C. for 120 minutes in the presence of sodium dodecyl sulfate conventionally used for denaturation of proteins. FIG. 20 shows the thermostability of the enzyme in the presence of each of the various surfactants, in which the ordinate indicates the residual activity ratio (%) and the abscissa indicates the period of time (minutes) for which the enzyme is treated at 90° C.

In FIG. 20, the open square indicates hexadecyl trimethyl ammonium bromide, the solid square indicates sodium dodecyl sulfate, the open circle indicates polyoxyethylene (20) sorbitan monolaurate, and the solid circle indicates sodium cholate.

(8) Substrate Specificity

Substrate specificity is able to be determined by using p-nitrophenol-derivatives as shown in Table 5. The method is conducted as follows. 1485 μl of 150 mM sodium citrate buffer solution (pH 5.0) containing the enzyme is added to a quartz cuvette for a spectrophotometer. 15 μl of 0.1M substrate solution shown in Table 5 is added to the enzyme solution and mixed. Immediately, reaction was detected by monitoring the change of absorbance at 410 nm versus time on a spectrophotometer. As a blank test, 1485 μl of 150 mM sodium citrate buffer (pH 5.0) not containing enzyme was used, and the determination described above was performed. In the test, reaction was performed at 90° C. One unit of enzyme activity was defined as that amount required to catalyze the release of 1 μmol p-nitrophenol per minute.

According to the method described above, hydrolytic activity towards p-nitrophenyl-β-D-glucopyranoside (GlcpβNp), p-nitrophenyl-β-D-galactopyranoside (GalpβNp), p-nitrophenyl-β-D-mannopyranoside (ManpβNp), p-nitrophenyl-β-D-xylopyranoside (XylpβNp), p-nitrophenyl-β-D-fucopyranoside (FucpβNp), p-nitrophenyl-α-D-galactopyranoside (GalpαNp) (all manufactured by Nacalai Tesque), was determined.

Results are shown in Table 5. Table 5 shows the specific activity (units/mg protein) towards the above-described substrates and the relative activity (%).

                  TABLE 5     ______________________________________     Specific activity of the enzyme                 Specific activity                             Relative activity     Substrate   (units/mg)  (%)     ______________________________________     GalpβNp                 192         100     GlcpβNp                 512         267     ManpβNp                 12.8        6.7     XylpβNp                 51.2        26.7     FucpβNp                 0           0     GalpαNp                 0           0     ______________________________________

Further, the enzymolytic activity of the enzyme was tested with the use of the following natural substrates. Specifically, each of lactose, cellobiose, methyl-β-D-glucose, salicin, arbutin, sucrose and maltose (all manufactured by Nacalai Tesque) as the substrate was dissolved in 1 ml of a 150 mM sodium citrate buffer (pH 5.0) in the final concentration of 50 mM. Each of carboxy methylcellulose (manufactured by Wako Pure Chemical Industries, Ltd.), Avicel (manufactured by Funakoshi Pharmaceutical Co., Ltd.) and laminarin (manufactured by Nacalai Tesque) was dissolved in the buffer in a final concentration of 17 g/l. Each of the above substrate solutions was heated to 90° C., and 15 μl (about 45 mU) of a phosphate (pH 7.0) of an enzyme was added thereto to effect a reaction at 90° C. for 30 minutes. The reaction was terminated by cooling with ice. The amount of glucose liberated in the reaction fluid was determined by the use of Glucose B Test Wako (manufactured by Wako Pure Chemical Industries, Ltd.).

Table 6 shows the relative activities (%) determined with respect to the other substrates when the lactose hydrolyzing activity is taken as 100%.

                  TABLE 6     ______________________________________     Substrate specificity ot the enzyme     Substrate        Relative activity (%)     ______________________________________     Lactose          100     Cellobiose       136     methyl-β-D-glucoside                      10.2     Salicin          69.6     Arbutin          6.1     Sucrose          1.9     Maltose          1.9     Carboxymethyl-cellulose                      0     Avicel           0     Laminarin        1.3     ______________________________________

(9) Characteristics of Amino Acid Sequence

With respect to the amino acid sequence (SEQ ID NO. 3) encoded by the β-galactosidase gene of the plasmid pTG2ES-105, an amino acid sequence homology search was carried out by the use of NBRF-PIR of DNASIS (manufactured by Hitachi Software Engineering).

The amino acid sequences of the present enzyme and the other hyperthermostable β-galactosidase (SEQ ID NO. 3) produced by Pyrococcus furiosus were compared with those of two types of thermostable β-galactosidases (SEQ ID NO. 5 and SEQ ID NO. 6) present in Sulfolobus solfataricus, and it has for the first time become apparent that, surprisingly, some of the sequences homologous between two types of thermostable enzymes are preserved in the hyperthermostable enzyme.

FIG. 21 and FIG. 22 are views comparing the amino acid sequences shown in SEQ ID NO. 1, SEQ ID NO. 3, SEQ ID NO. 5 and SEQ ID NO. 6. The ten different sequences each designated a "box sequence" by the inventors as indicated in the FIG. 21 and FIG. 22 (Box No. 1 to Box No. 10 as shown in SEQ ID NOS: 10-19, respectively) are the above-conserved sequences (see also SEQ ID Nos. 7-9 and 20-34, directed to the upper two amino acid sequences in Box No. 1 to Box No. 10).

Other hyperthermostable β-galactosidase genes can be cloned on the basis of the above sequences, for example, by the use of a primer or probe prepared from the amino acid sequences of the Box Nos. 7, 8 and 10 respectively defined by the SEQ ID NO. 7, SEQ ID NO. 8 and SEQ ID NO. 9.

In FIG. 21 and FIG. 22, the four rows of nucleotide sequences viewed from the top to the bottom respectively correspond to SEQ ID NO. 1 (top row), SEQ ID NO. 3 (second row), SEQ ID NO. 5 (third row) and SEQ ID NO. 6 (bottom row).

As described above in detail, the present invention provides a gene coding for a hyperthermostable β-galactosidase, including an SDS-resistant β-galactosidase, and a genetic engineering process for producing the hyperthermostable β-galactosidase by using this gene. This enzyme has a high thermostability and is useful particularly in food processing at high temperature and saccharide engineering.

The present invention further provides an EcoRI fragment of about 2.2 kbp which codes for the active center of the hyperthermostable β-galactosidase. Incubation of a transformant having a recombinant plasmid containing the above fragment transduced therein gives the hyperthermostable β-galactosidase. This enzyme is not only industrially applicable but is also useful in studies on the thermostabilities of enzymes, and the like.

Furthermore, the gene isolated in accordance with the present invention, or a gene consisting of a part thereof, is useful also as a probe in screening. The use of this gene as a probe makes it easy to clone hyperthermostable β-galactosidase genes hybridizable with this gene from a number of organisms.

Genes of all the enzymes analogous to the present enzyme which have sequences slightly different from that of the present enzyme but which are expected to have a similar enzymatic activity can be obtained by effecting hybridizations using the above obtained genes as the probe under strict conditions. The term "under strict conditions" as used herein means that the probe and hybridization of a nylon membrane having a DNA immobilized thereon are performed at 65° C. for 20 hr in a solution containing 6×SSC (1×SSC being a solution obtained by dissolving 8.76 g of sodium chloride and 4.41 g of sodium citrate in 1 l of water), 1% SDS, 100 μg/ml salmon sperm DNA and 5×Denhardt's (containing each of bovine serum albumin, polyvinyl pyrrolidone and ficoll in a concentration of 0.1%).

Also, genes of all the enzymes analogous to the present enzyme which have sequences slightly different from that of the present enzyme but which are expected to have a similar enzymatic activity can be obtained by effecting gene amplification using the above obtained genes as the primer.

Moreover, screening can be performed with the use of an oligomer, as a probe, having a nucleotide sequence encoding the above amino acid sequence jointly preserved by the thermostable β-galactosidase and the hyperthermostable β-galactosidase. That is, any of the thermostable and hyperthermostable genes of the enzymes analogous to the present enzyme which are expected to have the same enzymatic activity as that of the present enzyme can be obtained from the thermophilic and hyperthermophilic bacteria, respectively, by carrying out hybridizations in the hybridization solution having the same composition as that mentioned above at a temperature 5° C. lower than the value of Tm at which each oligomer forms a complementary strand with the target DNA. Still further, screening can be performed by effecting gene amplification with the use of the above oligomer as a primer.

Whether the gene obtained by the above screening is the gene of an enzyme analogous to the present enzyme which is expected to have the same enzymatic activity as that of the present enzyme can be ascertained in the following manner. The obtained gene is ligated to an expression vector ensuring expression in a suitable host according to the conventional procedure and introduced into the host to thereby obtain a transformant. This transformant is cultured, and the β-galactosidase activity of the culture or a cell-free extract therefrom is measured by the method described herein. Thus, it can be ascertained whether this gene is the gene of an enzyme analogous to the present enzyme which is expected to have the same enzymatic activity as that of the present enzyme, i.e., which has residual activity ratio of about 90% even after treatment at 90° C. for 120 minutes in the presence of SDS.

EXAMPLES

To further illustrate the present invention in greater detail, and not by way of limitation, the following Examples will be given.

Example 1

2 l of a medium comprising 1% of trypton, 0.5% of yeast extract, 1% of soluble starch, 3.5% of Jamarin S Solid (mfd. by Jamarin Laboratory), 0.5% of Jamarin S Liquid (mfd. by Jamarin Laboratory), 0.003% of MgSO₄, 0.001% of Nacl, 0.0001% of FeSO₄ ·7H₂ O, 0.0001% of CoSO₄, 0.0001% of CaCl₂ ·7H₂ O, 0.0001% of ZnSO₄, 0.1 ppm of CuSO₄ ·5H₂ O, 0.1 ppm of KAl(SO₄)₂, 0.1 ppm of H₃ BO₃, 0.1 ppm of Na₂ MoO₄ ·2H₂ O and 0.25 ppm of NiCl₂ ·6H₂ O was fed into a 2 l medium bottle and sterilized at 120° C. for 20 minutes. After eliminating the dissolved oxygen by blowing nitrogen gas, the medium was inoculated with the above-mentioned strain, which was then stationarily cultivated at 95° C. for 16 hours.

After completion of the cultivation, cells were collected by centrifuging. Then these cells were suspended in 30 ml of a 50 mM phosphate buffer solution (pH 7.0) containing 1 mM of EDTA, 1 mM of PMSF and 0.1% of Triton X-100 and disrupted by ultrasonication. This suspension of the disrupted cells was centrifuged at 4° C. at 12,000 rpm for 10 minutes and the supernatant was separated for use as a crude enzyme solution. When the content of the enzyme in this crude enzyme solution was measured, it was found out that 169.2 U of β-galactosidase was obtained.

The crude enzyme solution thus obtained was adsorbed by a DEAE Toyopearl M650 column (mfd. by Tosoh Corporation) which had previously been equilibrated with a 50 mM phosphate buffer solution (pH 7.0) containing 1 mM of EDTA. After washing this column with the above-mentioned buffer solution and developing with the same buffer solution by linear gradient elution with 0 to 0.5 M sodium chloride, two types of active fractions were eluted. These active fractions were named E-I and E-II fractions in order of elution. The active fractions were separately combined.

To the E-I fraction was added 3.6 M ammonium sulfate in such a manner as to give a concentration of 1.2 M. Then the obtained mixture was adsorbed by an HIC-Cartridge Column (mfd. by Bio-Rad) which had been previously equilibrated with a 50 mM phosphate buffer solution (pH 7.0) containing 1.2 M of ammonium sulfate and 1 mM of EDTA. After washing this column with a 50 mM phosphate buffer solution (pH 7.0) containing 1.2 M of ammonium sulfate and 1 mM of EDTA and developing with a 50 mM phosphate buffer solution (pH 7.0) containing 1 mM of EDTA by linear gradient elution with 1.2 to 0 M ammonium sulfate, active fractions were eluted. These active fractions were combined together, concentrated with Centriflo® CF25 (mfd. by Amicon) and MOLCUT II GC (mfd. by Millipore Corp.) and subjected to gel filtration by using a Superose 12 Column (mfd. by Pharmacia; 10×300 mm) which had been previously equilibrated with 50 mM phosphate buffer solution (pH 7.2) containing 100 mM of sodium chloride. Thus two active fractions were obtained and named E-I-1 and E-I-2 in order of elution. When the contents of enzymes in the fractions E-I-1 and E-I-2 were measured, it was found that 1.8 U of E-I-1 and 6.9 U of E-I-2 were obtained.

To the E-II fraction was added 3.6 M ammonium sulfate in such a manner as to give a concentration of 1.2 M. Then the obtained mixture was adsorbed by an HIC-Cartridge Column (mfd. by Bio-Rad) which had been previously equilibrated with a 50 mM phosphate buffer solution (pH 7.0) containing 1.2 M of ammonium sulfate and 1 mM of EDTA. After eluting this column with a 50 mM phosphate buffer solution (pH 7.0) containing 1.2 M of ammonium sulfate and 1 mM of EDTA, active fractions were eluted. These active fractions were combined together, concentrated with MOLCUT II GC (mfd. by Millipore Corp.) and subjected to gel filtration by using a Superose 12 Column (mfd. by Pharmacia: 10×300 mm) which had been previously equilibrated with a 50 mM phosphate buffer solution (pH 7.2) containing 100 mM of sodium chloride. When the content of the enzyme in the fraction E-II was measured, it was found that 3.4 U of the enzyme was obtained.

The active fractions were detected by measuring the activity of hydrolyzing o-nitrophenyl-β-D-galactopyranoside.

Example 2

By using the enzyme solutions as obtained in Example 1 above, effects of sodium dodecyl sulfate (SDS) on the enzymatic activities thereof were examined. As a buffer solution, McIlvaine's buffer solution of pH 6.0 was used for E-I-1 while McIlvaine's buffer solution of pH 6.6 was used for E-I-2 and E-II. 9.13 mU of E-I-1, 17.25 mU of E-I-2 and 11.35 mU of E-II were employed. To each enzyme was added the above-mentioned buffer solution containing 112 mM of 2-mercaptoethanol and 1 mM of magnesium chloride in such a manner as to give a total volume of 189 μl. After adding 10 μl of a 10% sodium dodecyl sulfate solution, 1 μl of a 0.4 M o-nitrophenyl-D-galactopyranoside solution was further added thereto to effect a reaction at 90° C. for 30 minutes. Then the reaction was stopped by adding 100 μl of a 0.1 M sodium carbonate solution. The amount of the o-nitrophenol thus formed was measured by monitoring the absorbance at 410 nm. As shown in Table 7, E-II, among the enzymes of the present invention, sustained its activity.

                  TABLE 7     ______________________________________     Influence of sodium dodecyl sulfate     on the activities of β-galactosidases                 Residual Activities (%)     Enzymes       SDS(+)   SDS(-)     ______________________________________     E-I-1         0        100     E-I-2         6.9      100     E-II          126.2    100     ______________________________________

Example 3

(1) Preparation of Pyrococcus furiosus Genome DNA

Pyrococcus furiosus DSM 3638 was incubated in the following manner. 2 l of a medium comprising 1% of trypton, 0.5% of yeast extract, 1% of soluble starch, 3.5% of Jamarin S Solid (mfd. by Jamarin Laboratory), 0.5% of Jamarin S Liquid (mfd. by Jamarin Laboratory), 0.003% of MgSO₄, 0.001% of NaCl, 0.0001% of FeSO₄ ·7H₂ O, 0.0001% of CoSO₄, 0.0001% of CaCl₂ ·7H₂ O, 0.0001% of ZnSO₄, 0.1 ppm of CuSO₄ ·5H₂ O, 0.1 ppm of KAl(SO₄)₂, 0.1 ppm of H₃ BO₃, 0.1 ppm of Na₂ MoO₄ ·2H₂ O and 0.25 ppm of NiCl₂ ·6H₂ O was fed into a 2 l medium bottle and sterilized at 120° C. for 20 minutes. After eliminating the dissolved oxygen by blowing nitrogen gas, the medium was inoculated with the above-mentioned strain, which was then stationarily incubated at 95° C. for 16 hours. After the completion of the incubation, cells were collected by centrifuging.

Then the collected cells were suspended in 4 ml of a 0.05 M Tris-HCl (pH 8.0) containing 25% of sucrose. To the obtained suspension were added 0.8 ml of lysozyme 5 mg/ml, 0.25 M Tris-HCl (pH 8.0)! and 2 ml of 0.2 M EDTA. After maintaining at 20° C. for 1 hour, 24 ml of an SET solution 150 mM Nacl, 1 mM EDTA, 20 mM Tris-HCl (pH 8.0)! was added. Further, 4 ml of 5% SDS and 400 μl of proteinase K (10 mg/ml) were added thereto, followed by a reaction at 37° C. for 1 hour. After the completion of the reaction, the reaction mixture was extracted with chloroform/phenol and precipitated from ethanol. Thus approximately 3.2 mg of a genome DNA was prepared.

(2) Preparation of Cosmid Protein Library

400 μg of the Pyrococcus furiosus DSM 3638 genome DNA was partially digested with Sau 3AI in a buffer solution for Sau 3AI 50 mM Tris-HCl (pH 7.5), 10 mM MgCl₂, 1 mM dithio-threitol, 100 mM Nacl! and fractionated according to the size by density gradient centrifugation. One μg of Triple Helix Cosmid Vector was cleaved with Bam HI and mixed with 140 μg of the genome DNA fragments of 35 to 50 kbp which had been obtained by the fractionation as described above. After ligating with the use of a Ligation Kit (mfd. by Takara Shuzo Co., Ltd.), the Pyrococcus genome DNA fragments were packaged into λ-phage particles by the in vitro packaging method using Gigapack II Gold (mfd. by Stratagene). By using a part of the phage solution thus obtained, E. coli DH5αMCR was transformed to thereby give a cosmid library.

From several colonies thus obtained, cosmid DNAs were prepared and it was confirmed that they had an inserted fragment of an appropriate size in common. Next, 500 colonies were suspended in 2 ml of an L-broth medium containing 0.01% of ampicillin and incubated under shaking at 37° C. for 16 hours. The culture was centrifuged and cells were collected as a precipitate. These cells were suspended in 20 mM Tris-HCl (pH 8.0) and thermally treated at 100° C. for 10 minutes. Subsequently, they were ultrasonicated and further thermally treated at 100° C. for 10 minutes. After centrifuging, the supernatant was collected and referred to as a crude enzyme solution. Thus 500 cosmid protein libraries were prepared.

(3) Selection of cosmid containing β-galactosidase gene

The cosmid protein libraries obtaining in the above Example 3-(2) were divided into 50 groups each having 10 cosmid protein libraries. Then the β-galactosidase activity of the crude enzyme solution of each protein library group was determined. Namely, 10 μl of the crude enzyme solution was added to 99.5 μl of a 100 mM phosphate buffer solution (pH 7.3) containing 112 mM of 2-mercaptoethanol and 1 mM of magnesium chloride. After adding 0.5 μl of a dimethyl sulfoxide solution containing 0.4 M of o-nitrophenyl-β-D-galactopyranoside, the mixture was reacted at 95° C. for 30 minutes. Then the reaction was stopped by adding 50 μl of 0.1 M sodium carbonate and the absorbance at 410 nm was measured. Thus the amount of the formed o-nitrophenol was determined.

Next, β-galactosidase activities of 60 protein libraries constituting six groups of the cosmid protein libraries showing β-galactosidase activity were further measured. Thus seven cosmid proteins having β-galactosidase activity were specified and seven could DNAs corresponding thereto were specified.

(4) Preparation of plasmid pTGE-101 and production of thermostable β-galactosidase

Seven cosmid DNAs obtained in the above Example 3-(3) were completely digested with a restriction enzyme EcoRI and electrophoresed on a gel. Thus an EcoRI DNA fragment of about 2.2 kbp which was common to these seven cosmid DNAs was purified. Then a vector pUC19 was cleaved at the EcoRI site and dephosphorylated at the end. Then the above-mentioned EcoRI DNA fragment of about 2.2 kbp was ligated onto this plasmid with the use of a ligation kit. By using the reaction mixture thus obtained, E. coli JM109 was transformed. Then a DNA was extracted from the transformant, cleaved with EcoRI and electrophoresed on an agarose gel. Thus the presence of the EcoRI fragment of about 2.2 kpb inserted thereinto was confirmed. The obtained plasmid and the transformant were named respectively pTGE-101 and Escherichia coli JM109/pTGE-101.

This EcoRI DNA fragment of about 2.2 kpb was cleaved with several restriction enzymes and analyzed by agarose gel electrophoresis. FIG. 6 shows a restriction enzyme map of the obtained plasmid pTGE-101 having the EcoRI DNA fragment of about 2.2 kbp.

Escherichia coli JM109/pTGE-101 was suspended in 5 ml of an L-broth medium containing 0.01% of ampicillin and incubated under shaking at 37° C. for 16 hours. The culture was centrifuged and the cells thus collected were suspended in a 50 mM phosphate buffer solution (pH 7.0) containing 1 mM of EDTA and thermally treated at 100° C. for 10 minutes. Then the cells were ultrasonicated and further treated at 100° C. for 10 minutes. After centrifuging, the supernatant was separated for use as a crude enzyme solution. Then the β-galactosidase activity was determined in accordance with the method as described in the above Example 3-(3) except that 5 μl of this crude enzyme solution was used. As a result, this crude enzyme solution showed no activity. Then another crude enzyme solution was prepared in the same manner as the one described above except that the thermal treatments (100° C., 10 minutes, twice) were omitted. Then the β-galactosidase activity of the crude enzyme solution was determined in accordance with the method of Example 3-(3) except that the reaction temperature was adjusted to 70° C. This crude enzyme solution had an activity of decomposing o-nitrophenyl-β-D-galactopyranoside at pH 7.3 at 70° C. Namely, a gene coding for a thermostable β-galactosidase showing an activity at 70° C. had been inserted into pTGE-101.

(5) Preparation of plasmid pTGH-301

The EcoRI DNA fragment (about 2.2 kbp) obtained in the above Example 3-(4) was labeled with (α-³² P) dCTP (3000 Ci/mmol; mfd. by Amersham) by using a Random Primer Labeling Kit (mfd. by Takara Shuzo Co., Ltd.). By using the labeled DNA fragment thus obtained as a probe, the cosmid DNAs as specified in the above Example 3-(3), which had been completely digested with Hind III and separated by electrophoresis, were analyzed by Southern hybridization. Thus a Hind III DNA fragment of about 3.5 kbp hybridized by the above probe was identified and purified. Next, pUC19 was cleaved at the Hind III site and dephosphorylated at the end. The above-mentioned Hind III DNA fragment was ligated onto this plasmid by using a ligation kit and E. coli JM109 was transformed thereby. The obtained plasmid was named plasmid pTGH-301, while the transformant was named Escherichia coli JM109/pTGH-301.

Escherichia coli JM109/pTGH-301 was suspended in 5 ml of an L-broth medium containing 0.01% of ampicillin and incubated under shaking at 37° C. for 16 hours. The culture was centrifuged and the cells thus collected were suspended in a 50 mM phosphate buffer solution (pH 7.0) containing 1 mM of EDTA and thermally treated at 100° C. for 10 minutes. Subsequently, the cells were ultrasonicated and then thermally treated again at 100° C. for 10 minutes. After centrifuging, the supernatant was separated for use as a crude enzyme solution. The β-galactosidase activity was determined in accordance with the method of the above Example 3-(3) except that 5 μl of this crude enzyme solution was used. As a result, the activity of a hyperthermostable β-galactosidase which can withstand the thermal treatment at 100° C. for 20 minutes was observed in the crude enzyme solution.

The above-mentioned Hind III DNA fragment of about 3.5 kbp was cleaved with several restriction enzymes and analyzed by agarose gel electrophoresis. FIG. 7 shows a restriction enzyme map of the plasmid pTGH-301 containing the Hind III DNA fragment (about 3.5 kpb) obtained above. E. coli JM109 transformed by the plasmid pTGH-301 containing the hyperthermostable β-galactosidase gene was expressed as Escherichia coli JM109/pTGH-301 and has been deposited with Fermentation Research Institute of the Agency of Industrial Science and Technology under the accession number FERM P-13348.

(6) Preparation of plasmid pTCEH-401

The above-mentioned plasmid pTGH-301 was digested with EcoRI and electrophoresed on an agarose gel. Among DNA fragments of about 3.0 kbp, about 2.2 kbp and about 1.0 kbp thus separated, two DNA fragments (of about 3.0 kbp and about 2.2 kbp) were recovered. The DNA fragment of about 3.0 kbp was dephosphorylated with the use of alkaline phosphatase (mfd. by Takara Shuzo Co., Ltd.) and ligated by mixing with the DNA fragment of about 2.2 kbp, followed by transduction into E. coli JM109. The hyperthermostable β-galactosidase activities of the colonies thus formed were determined. From colonies showing the activity, a plasmid was prepared and named pTGEH-401. E. coli JM109 containing this plasmid was named Escherichia coli JM109/pTGEH-401, and deposited at the National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology, Japan, under the accession number of FERM BP-4468.

FIG. 8 shows a restriction enzyme map of the plasmid pTGEH-401. FIG. 9 shows a restriction enzyme map of the hyperthermostable β-galactosidase gene of about 2.5 kbp, which originates in Pyrococcus furiosus and is obtained in accordance with the present invention, inserted into the plasmid pTGEH-401.

Example 4

Determination of DNA sequence of the hyperthermostable β-galactosidase gene

The DNA fragment of about 3.5 kbp containing the hyperthermostable β-galactosidase gene inserted in the plasmid pTGH-301 was cleaved with several restriction enzymes and subcloned into plasmid vector pUC118. The DNA sequences of each fragment subcloned were determined by the dideoxy method using BcaBest™ Dideoxy Sequencing Kit (mfd. by Takara Shuzo, Co., LTD.). SEQ ID NO. 2 in the Sequence Listing shows the DNA sequence of the DNA fragment containing the hyperthermostable β-galactosidase gene which has been inserted in the plasmid pTGH-301. SEQ ID NO. 1 in the Sequence Listing shows the amino acid sequence of the hyperthermostable β-galactosidase which is deduced from the DNA sequence shown in SEQ ID NO. 2.

Example 5

Production of hyperthermostable β-galactosidase

Escherichia coli JM109/pTGH-301 (FERM P-13348) having the plasmid pTGH-301 containing the hyperthermostable β-galactosidase gene of the present invention transduced therein, which was obtained in the above Example 3, was suspended in 5 ml of an L-broth medium containing 0.01% of ampicillin and incubated under shaking at 37° C. for 16 hours. Then the culture was suspended in 1.2 l of a medium of the same conditions and incubated under shaking at 37° C. for 16 hours. After centrifuging the culture, the cells thus collected were suspended in a 50 mM phosphate buffer solution (pH 7.0) containing 1 mM of EDTA and thermally treated at 100° C. for 10 minutes.

Next, the cells were ultrasonicated and thermally treated again at 100° C. for 10 minutes. After centrifuging, the supernatant was separated for use as a crude enzyme solution. This crude enzyme solution had 20 U of o-nitrophenyl-β-D-galactopyranoside-decomposing activity per ml of the L-broth medium at pH 7.3 at 95° C. This crude enzyme solution was concentrated with MOLCUT II (cutoff molecular weight: 10,000, mfd. by Millipore Corp.) and gel-filtered through a Superose 12 Column (10×300 mm; mfd. by Pharmacia), which had been equilibrated with a 50 mM phosphate buffer solution (pH 7.2) containing 100 mM of NaCl, and an active fraction was collected. The active fraction was concentrated with MOLCUT II (cutoff molecular weight: 10,000; mfd. by Millipore Corp.) and adsorbed by 1 ml of an APTG affinity column (mfd. by MoBi Tec), which had been equilibrated with a 20 mM glycine sodium buffer solution (pH 7.5) containing 10 mM of MgCl₂, and 200 mM of NaCl. After maintaining at room temperature for 1 hour, the column was washed with 12.5 ml of a 20 mM glycine sodium buffer solution (pH 7.5) containing 10 mM of MgCl₂, and 200 mM of NaCl and then eluted with a 100 mM glycine sodium buffer solution (pH 10.0). An active fraction was separated and thus a purified enzyme preparation was obtained. When electrophoresed on a 7.5% SDS-polyacrylamide gel, this preparation showed a single band.

Similarly, Escherichia coli JM109/pTGEH-401 having the plasmid pTGEH-401 containing the hyperthermostable β-galactosidase gene of the present invention transduced therein was incubated in the same manner as the one described above. From the culture, an active fraction of the hyperthermostable β-galactosidase was purified and thus a hyperthermostable β-galactosidase preparation was obtained.

Example 6

(1) Preparation of Pyrococcus furiosus genome DNA

Pyrococcus furiosus DSM 3638 was incubated in the following manner. 2 l of a medium comprising 1% trypton, 0.5% yeast extract, 1% soluble starch, 3.5% Jamarin S Solid (manufactured by Jamarin Laboratory), 0.5% Jamarin S Liquid (manufactured by Jamarin Laboratory), 0.003% MgSO₄, 0.001% NaCl, 0.0001% FeSO₄ ·7H₂ O, 0.0001% CoCO₄, 0.0001% CaCl₂ ·7H₂ O, 0.0001% ZnSO₄, 0.1 ppm CuSO₄ ·5H₂ O, 0.1 ppm KAl(SO₄)₂, 0.1 ppm H₃ BO₃, 0.1 ppm Na₂ MoO₄ ·2H₂ O and 0.25 ppm NiCl₂ ·6H₂ O was fed into a 2 l medium bottle and sterilized at 120° C. for 20 minutes. After eliminating the dissolved oxygen by blowing nitrogen gas, the medium was inoculated with the above-mentioned strain, which was then stationarily incubated at 95° C. for 16 hours. After the completion of the incubation, cells were collected by centrifuging.

Then the collected cells were suspended in 4 ml of a 0.05 M Tris-HCl (pH 8.0) containing 25% sucrose. To the obtained suspension were added 0.8 ml of lysozyme 5 mg/ml, 0.25 M Tris-HCl (pH 8.0)! and 2 ml of 0.2 M EDTA. After maintaining at 20° C. for 1 hour, 24 ml of an SET solution 150 mM NaCl, 1 mM EDTA, 20 mM Tris-HCl (pH 8.0)! was added. Further, 4 ml of 5% SDS and 400 μl of proteinase K (10 mg/ml) were added thereto, followed by reaction at 37° C. for 1 hour. After the completion of the reaction, the reaction mixture was extracted with chloroform/phenol and precipitated from ethanol. Thus approximately 3.2 mg of genome DNA was prepared.

(2) Preparation of cosmid protein library

400 μg of the Pyrococcus furiosus DSM 3638 genome DNA was partially digested with Sau 3AI in a buffer solution for Sau 3AI 50 mM Tris-HCl (pH 7.5), 10 mM MgCl₂, 1 mM dithiothreitol, 100 mM NaCl! and fractionated according to size by density gradient centrifugation. 1 μg of Triple Helix Cosmid Vector was cleaved with Bam HI and mixed with 140 μg of the genome DNA fragments of 35 to 50 kbp which had been obtained by the fractionation as described above. After ligating with the use of a Ligation Kit (manufactured by Takara Shuzo Co., Ltd.), the Pyrococcus genome DNA fragments were packaged into λ-phage particles by the in vitro packaging method using Gigapack II Gold (manufactured by Strategene). By using a part of the phage solution thus obtained, Escherichia coli DH5αMCR was transformed to thereby give a cosmid library.

From several colonies thus obtained, cosmid DNAs were prepared and it was confirmed that they had an inserted fragment of an appropriate size in common. Next, 500 colonies were suspended in 2 ml of an L-broth medium containing 0.01% of ampicillin and incubated with shaking at 37° C. for 16 hours. The culture was centrifuged and cells were collected as a precipitate. These cells were suspended in 20 mM Tris-HCl (pH 8.0) and thermally treated at 100° C. for 10 minutes. Subsequently, they were ultrasonicated and further thermally treated at 100° C. for 10 minutes. After centrifuging, the supernatant was collected and referred to as a crude enzyme solution. Thus 500 cosmid protein libraries were prepared.

(3) Selection of cosmid containing β-galactosidase gene

The β-galactosidase activity of the crude enzymatic solution of the 500 cosmid protein library obtained in Example 6-(2) was determined. Specifically, 10 μl of the crude enzymatic solution was added to 99.5 μl of a 100 mM phosphate buffer (pH 7.0) containing 112 mM 2-mercaptoethanol, 1 mM magnesium chloride and 1% SDS. Subsequently, 0.5 μl of a dimethyl sulfoxide solution containing 0.4 M o-nitrophenyl-β-D-galactopyranoside was added and reacted at 95° C. for 30 minutes. This reaction was terminated by adding 50 μl of 0.1 M sodium carbonate. The absorbance at 410 nm was measured, thereby determining the amount of the formed o-nitrophenol.

One cosmid protein with β-galactosidase activity was selected from the 500 cosmid protein library, and one cosmid DNA corresponding thereto was identified.

(4) Preparation of plasmid pTG2S-112 and production of thermostable β-galactosidase

The single cosmid DNA obtained in Example 6-(3) was completely digested with the restriction enzyme Sma I. Separately, pUC18 as a vector was cleaved at its Sma I site, followed by end dephosphorylation. The above Sma I digested DNA fragment was ligated to the vector plasmid by the use of a ligation kit. The Escherichia coli JM109 was transformed with the use of the resultant reaction solution. The transformant was suspended in 5 ml of an L-broth medium containing 0.01% ampicillin and cultured while shaking at 37° C. for 16 hr. The resultant culture was centrifuged, and the recovered cells were suspended in a 50 mM phosphate buffer (pH 7.0) containing 1 mM EDTA. The suspension was heated at 100° C. for 10 minutes, sonicated, further heated at 100° C. for 10 minutes, and centrifuged to thereby obtain a supernatant as a crude enzymatic solution. The β-galactosidase activity was assayed by the same activity assay method as that of Example 6-(3) except that 5 μl of this crude enzymatic solution was used. The hyperthermostable β-galactosidase activity exhibiting resistance to heat treatment at 100° C. for 20 minutes was recognized in the crude enzymatic solution.

The plasmid corresponding to this crude enzymatic solution was designated plasmid pTG2S-112. The plasmid pTG2S-112 was introduced into the Escherichia coli JM109, thereby obtaining a transformant. This transformant was designated as Escherichia coli JM109/pTG2S-112.

(5) Preparation of plasmid pTG2ES-105

The plasmid pTG2S-112 containing the Sma I DNA fragment of about 4 kbp obtained in Example 6-(4) was completely digested with the restriction enzymes Eco81I and Kpn I. The resultant Eco81I-Kpn I DNA fragment of about 4.7 kbp was purified, blunt-ended and self-ligated.

The obtained plasmid was designated plasmid pTG2ES-105. This plasmid was introduced into the Escherichia coli JM109, thereby obtaining a transformant. This transformant was designated as Escherichia coli JM109/pTG2ES-105. This strain was deposited on Apr. 20, 1994 at the National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology (1-3, Higashi 1 Chome Tsukuba-shi Ibaraki-ken 305, JAPAN) under the accession number FERM BP-5023.

FIG. 14 shows a restriction enzyme cleavage map of the plasmid pTG2ES-105, and FIG. 15 shows a restriction enzyme cleavage map of the hyperthermostable β-galactosidase gene of about 2.0 kbp obtained according to the present invention which was derived from Pyrococcus furiosus and inserted in the plasmid pTG2ES-105.

Example 7

Determination of nucleotide sequence of hyperthermostable β-galactosidase gene

Deletion mutants were prepared from the above fragment of about 2.0 kbp including the hyperthermostable β-galactosidase gene inserted in the plasmid pTG2ES-105 with the use of Deletion Kit for Kilo Sequence (manufactured by Takara Shuzo Co., Ltd.), and the nucleotide sequences of the resultant fragments were determined.

The determination of the nucleotide sequences was conducted by the dideoxy method in which use was made of the Bca Bast Dideoxy Sequencing Kit (manufactured by Takara Shuzo Co., Ltd.).

SEQ ID NO. 4 shows the nucleotide sequence of the DNA fragment including the hyperthermostable β-galactosidase gene inserted in the plasmid pTG2ES-105. SEQ ID NO. 3 shows the amino acid sequence of the hyperthermostable β-galactosidase encoded by the above nucleotide sequence.

Example 8

(1) Production of hyperthermostable β-galactosidase

The Escherichia coli JM109/pTG2ES-105 (FERM BP-5023) obtained in Example 6, into which the plasmid pTG2ES-105 containing the hyperthermostable β-galactosidase gene of the present invention had been introduced, was suspended in 5 ml of an L-broth medium containing 0.01% ampicillin and cultured while shaking at 37° C. for 16 hr. The culture was suspended in 1.2 l of the medium of the same composition and cultured while shaking at 37° C. for 16 hr. The resultant culture was centrifuged, and the recovered cells were suspended in a 50 mM phosphate buffer (pH 7.0) containing 1 mM EDTA. The suspension was heated at 100° C. for 10 minutes, sonicated, further heated at 100° C. for 10 minutes, and centrifuged to thereby obtain a supernatant as a crude enzymatic solution.

The specific activity of β-galactosidase in the crude enzymatic solution was about 740 units/mg at pH 5.0 and 90° C.

EFFECTS OF THE INVENTION

The present invention provides hyperthermostable β-galactosidases and further provides a β-galactosidase having a hyperthermostability that can exert its action even in the presence of sodium dodecyl sulfate which is a powerful surfactant. The use of the hyperthermostable β-galactosidase gene of the present invention makes it possible to industrially produce a hyperthermostable β-galactosidase. By using the hyperthermostable β-galactosidase gene of the present invention or part thereof as a probe, hyperthermostable β-galactosidase genes originating in various organisms can be obtained.

    __________________________________________________________________________     #             SEQUENCE LISTING     - (1) GENERAL INFORMATION:     -    (iii) NUMBER OF SEQUENCES:  34     - (2) INFORMATION FOR SEQ ID NO:1:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  510 ami - #no acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (vi) ORIGINAL SOURCE:               (A) ORGANISM:  Pyrococc - #us furiosus     #ID NO:1: (xi) SEQUENCE DESCRIPTION: SEQ     -      Met Phe Pro Glu Lys Phe Leu Trp - # Gly Val Ala Gln Ser Gly Phe     #    15     -      Gln Phe Glu Met Gly Asp Lys Leu - # Arg Arg Asn Ile Asp Thr Asn     #    30     -      Thr Asp Trp Trp His Trp Val Arg - # Asp Lys Thr Asn Ile Glu Lys     #    45     -      Gly Leu Val Ser Gly Asp Leu Pro - # Glu Glu Gly Ile Asn Asn Tyr     #    60     -      Glu Leu Tyr Glu Lys Asp His Glu - # Ile Ala Arg Lys Leu Gly Leu     #    75     -      Asn Ala Tyr Arg Ile Gly Ile Glu - # Trp Ser Arg Ile Phe Pro Trp     #    90     -      Pro Thr Thr Phe Ile Asp Val Asp - # Tyr Ser Tyr Asn Glu Ser Tyr     #   105     -      Asn Leu Ile Glu Asp Val Lys Ile - # Thr Lys Asp Thr Leu Glu Glu     #   120     -      Leu Asp Glu Ile Ala Asn Lys Arg - # Glu Val Ala Tyr Tyr Arg Ser     #   135     -      Val Ile Asn Ser Leu Arg Ser Lys - # Gly Phe Lys Val Ile Val Asn     #   150     -      Leu Asn His Phe Thr Leu Pro Tyr - # Trp Leu His Asp Pro Ile Glu     #   165     -      Ala Arg Glu Arg Ala Leu Thr Asn - # Lys Arg Asn Gly Trp Val Asn     #   180     -      Pro Arg Thr Val Ile Glu Phe Ala - # Lys Tyr Ala Ala Tyr Ile Ala     #   195     -      Tyr Lys Phe Gly Asp Ile Val Asp - # Met Trp Ser Thr Phe Asn Glu     #   210     -      Pro Met Val Val Val Glu Leu Gly - # Tyr Leu Ala Pro Tyr Ser Gly     #   225     -      Phe Pro Pro Gly Val Leu Asn Pro - # Glu Ala Ala Lys Leu Ala Ile     #   240     -      Leu His Met Ile Asn Ala His Ala - # Leu Ala Tyr Arg Gln Ile Lys     #   255     -      Lys Phe Asp Thr Glu Lys Ala Asp - # Lys Asp Ser Lys Glu Pro Ala     #   270     -      Glu Val Gly Ile Ile Tyr Asn Asn - # Ile Gly Val Ala Tyr Pro Lys     #   285     -      Asp Pro Asn Asp Ser Lys Asp Val - # Lys Ala Ala Glu Asn Asp Asn     #   300     -      Phe Phe His Ser Gly Leu Phe Phe - # Glu Ala Ile His Lys Gly Lys     #   315     -      Leu Asn Ile Glu Phe Asp Gly Glu - # Thr Phe Ile Asp Ala Pro Tyr     #   330     -      Leu Lys Gly Asn Asp Trp Ile Gly - # Val Asn Tyr Tyr Thr Arg Glu     #   345     -      Val Val Thr Tyr Gln Glu Pro Met - # Phe Pro Ser Ile Pro Leu Ile     #   360     -      Thr Phe Lys Gly Val Gln Gly Tyr - # Gly Tyr Ala Cys Arg Pro Gly     #   375     -      Thr Leu Ser Lys Asp Asp Arg Pro - # Val Ser Asp Ile Gly Trp Glu     #   390     -      Leu Tyr Pro Glu Gly Met Tyr Asp - # Ser Ile Val Glu Ala His Lys     #   405     -      Tyr Gly Val Pro Val Tyr Val Thr - # Glu Asn Gly Ile Ala Asp Ser     #   420     -      Lys Asp Ile Leu Arg Pro Tyr Tyr - # Ile Ala Ser His Ile Lys Met     #   435     -      Ile Glu Lys Ala Phe Glu Asp Gly - # Tyr Glu Val Lys Gly Tyr Phe     #   450     -      His Trp Ala Leu Thr Asp Asn Phe - # Glu Trp Ala Leu Gly Phe Arg     #   465     -      Met Arg Phe Gly Leu Tyr Glu Val - # Asn Leu Ile Thr Lys Glu Arg     #   480     -      Ile Pro Arg Glu Lys Ser Val Ser - # Ile Phe Arg Glu Ile Val Ala     #   495     -      Asn Asn Gly Val Thr Lys Lys Ile - # Glu Glu Glu Leu Leu Arg Gly     #   510     - (2) INFORMATION FOR SEQ ID NO:2:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  1533 ba - #se pairs               (B) TYPE:  nucleic a - #cid               (C) STRANDEDNESS:  doub - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE:  genomic DNA     -    (iii) HYPOTHETICAL:  NO     -     (iv) ANTI-SENSE:  NO     -     (vi) ORIGINAL SOURCE:               (A) ORGANISM:  Pyrococc - #us furiosus     #ID NO:2: (xi) SEQUENCE DESCRIPTION: SEQ     - ATGTTCCCTG AAAAGTTCCT TTGGGGTGTG GCACAATCGG GTTTTCAGTT TG - #AAATGGGG       60     - GATAAACTCA GGAGGAATAT TGACACTAAC ACTGATTGGT GGCACTGGGT AA - #GGGATAAG      120     - ACAAATATAG AGAAAGGCCT CGTTAGTGGA GATCTTCCCG AGGAGGGGAT TA - #ACAATTAC      180     - GAGCTTTATG AGAAGGACCA TGAGATTGCA AGAAAGCTGG GTCTTAATGC TT - #ACAGAATA      240     - GGCATAGAGT GGAGCAGAAT ATTCCCATGG CCAACGACAT TTATTGATGT TG - #ATTATAGC      300     - TATAATGAAT CATATAACCT TATAGAAGAT GTAAAGATCA CCAAGGACAC TT - #TGGAGGAG      360     - TTAGATGAGA TCGCCAACAA GAGGGAGGTG GCCTACTATA GGTCAGTCAT AA - #ACAGCCTG      420     - AGGAGCAAGG GGTTTAAGGT TATAGTTAAT CTAAATCACT TCACCCTTCC AT - #ATTGGTTG      480     - CATGATCCCA TTGAGGCTAG GGAGAGGGCG TTAACTAATA AGAGGAACGG CT - #GGGTTAAC      540     - CCAAGAACAG TTATAGAGTT TGCAAAGTAT GCCGCTTACA TAGCCTATAA GT - #TTGGAGAT      600     - ATAGTGGATA TGTGGAGCAC GTTTAATGAG CCTATGGTGG TTGTTGAGCT TG - #GCTACCTA      660     - GCCCCCTACT CTGGCTTCCC TCCAGGGGTT CTAAATCCAG AGGCCGCAAA GC - #TGGCGATA      720     - CTTCACATGA TAAATGCACA TGCTTTAGCT TATAGGCAGA TAAAGAAGTT TG - #ACACTGAG      780     - AAAGCTGATA AGGATTCTAA AGAGCCTGCA GAAGTTGGTA TAATTTACAA CA - #ACATTGGA      840     - GTTGCTTATC CCAAGGATCC GAACGATTCC AAGGATGTTA AGGCAGCAGA AA - #ACGACAAC      900     - TTCTTCCACT CAGGGCTGTT CTTCGAGGCC ATACACAAAG GAAAACTTAA TA - #TAGAGTTT      960     - GACGGTGAAA CGTTTATAGA TGCCCCCTAT CTAAAGGGCA ATGACTGGAT AG - #GGGTTAAT     1020     - TACTACACAA GGGAAGTAGT TACGTATCAG GAACCAATGT TTCCTTCAAT CC - #CGCTGATC     1080     - ACCTTTAAGG GAGTTCAAGG ATATGGCTAT GCCTGCAGAC CTGGAACTCT GT - #CAAAGGAT     1140     - GACAGACCCG TCAGCGACAT AGGATGGGAA CTCTATCCAG AGGGGATGTA CG - #ATTCAATA     1200     - GTTGAAGCTC ACAAGTACGG CGTTCCAGTT TACGTGACGG AGAACGGAAT AG - #CGGATTCA     1260     - AAGGACATCC TAAGACCTTA CTACATAGCG AGCCACATAA AGATGATAGA GA - #AGGCCTTT     1320     - GAGGATGGGT ATGAAGTTAA GGGCTACTTC CACTGGGCAT TAACTGACAA CT - #TCGAGTGG     1380     - GCTCTCGGGT TTAGAATGCG CTTTGGCCTC TACGAAGTCA ACCTAATTAC AA - #AGGAGAGA     1440     - ATTCCCAGGG AGAAGAGCGT GTCGATATTC AGAGAGATAG TAGCCAATAA TG - #GTGTTACG     1500     #       1533       AATT GCTGAGGGGA TGA     - (2) INFORMATION FOR SEQ ID NO:3:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  491 ami - #no acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:3: (xi) SEQUENCE DESCRIPTION: SEQ     -      Met Lys Phe Pro Lys Asn Phe Met - # Phe Gly Tyr Ser Trp Ser Gly     #    15     -      Phe Gln Phe Glu Met Gly Leu Pro - # Gly Ser Glu Val Glu Ser Asp     #    30     -      Trp Trp Val Trp Val His Asp Lys - # Glu Asn Ile Ala Ser Gly Leu     #    45     -      Val Ser Gly Asp Leu Pro Glu Asn - # Gly Pro Ala Tyr Trp His Leu     #    60     -      Tyr Lys Gln Asp His Asp Ile Ala - # Glu Lys Leu Gly Met Asp Cys     #    75     -      Ile Arg Gly Gly Ile Glu Trp Ala - # Arg Ile Phe Pro Lys Pro Thr     #    90     -      Phe Asp Val Lys Val Asp Val Glu - # Lys Asp Glu Glu Gly Asn Ile     #   105     -      Ile Ser Val Asp Val Pro Glu Ser - # Thr Ile Lys Glu Leu Glu Lys     #   120     -      Ile Ala Asn Met Glu Ala Leu Glu - # His Tyr Arg Lys Ile Tyr Ser     #   135     -      Asp Trp Lys Glu Arg Gly Lys Thr - # Phe Ile Leu Asn Leu Tyr His     #   150     -      Trp Pro Leu Pro Leu Trp Ile His - # Asp Pro Ile Ala Val Arg Lys     #   165     -      Leu Gly Pro Asp Arg Ala Pro Ala - # Gly Trp Leu Asp Glu Lys Thr     #   180     -      Val Val Glu Phe Val Lys Phe Ala - # Ala Phe Val Ala Tyr His Leu     #   195     -      Asp Asp Leu Val Asp Met Trp Ser - # Thr Met Asn Glu Pro Asn Val     #   210     -      Val Tyr Asn Gln Gly Tyr Ile Asn - # Leu Arg Ser Gly Phe Pro Pro     #   225     -      Gly Tyr Leu Ser Phe Glu Ala Ala - # Glu Lys Ala Lys Phe Asn Leu     #   240     -      Ile Gln Ala His Ile Gly Ala Tyr - # Asp Ala Ile Lys Glu Tyr Ser     #   255     -      Glu Lys Ser Val Gly Val Ile Tyr - # Ala Phe Ala Trp His Asp Pro     #   270     -      Leu Ala Glu Glu Tyr Lys Asp Glu - # Val Glu Glu Ile Arg Lys Lys     #   285     -      Asp Tyr Glu Phe Val Thr Ile Leu - # His Ser Lys Gly Lys Leu Asp     #   300     -      Trp Ile Gly Val Asn Tyr Tyr Ser - # Arg Leu Val Tyr Gly Ala Lys     #   315     -      Asp Gly His Leu Val Pro Leu Pro - # Gly Tyr Gly Phe Met Ser Glu     #   330     -      Arg Gly Gly Phe Ala Lys Ser Gly - # Arg Pro Ala Ser Asp Phe Gly     #   345     -      Trp Glu Met Tyr Pro Glu Gly Leu - # Glu Asn Leu Leu Lys Tyr Leu     #   360     -      Asn Asn Ala Tyr Glu Leu Pro Met - # Ile Ile Thr Glu Asn Gly Met     #   375     -      Ala Asp Ala Ala Asp Arg Tyr Arg - # Pro His Tyr Leu Val Ser His     #   390     -      Leu Lys Ala Val Tyr Asn Ala Met - # Lys Glu Gly Ala Asp Val Arg     #   405     -      Gly Tyr Leu His Trp Ser Leu Thr - # Asp Asn Tyr Glu Trp Ala Gln     #   420     -      Gly Phe Arg Met Arg Phe Gly Leu - # Val Tyr Val Asp Phe Glu Thr     #   435     -      Lys Lys Arg Tyr Leu Arg Pro Ser - # Ala Leu Val Phe Arg Glu Ile     #   450     -      Ala Thr Gln Lys Glu Ile Pro Glu - # Glu Leu Ala His Leu Ala Asp     #   465     -      Leu Lys Phe Val Thr Lys Lys Val - # Ala Ile Ser Phe Phe Leu Cys     #   480     -      Phe Leu Thr His Ile Phe Gly Lys - # Ile Arg Ser     #   490     - (2) INFORMATION FOR SEQ ID NO:4:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  1476 ba - #se pairs               (B) TYPE:  nucleic a - #cid               (C) STRANDEDNESS:  doub - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE:  genomic DNA     #ID NO:4: (xi) SEQUENCE DESCRIPTION: SEQ     - ATGAAGTTCC CAAAAAACTT CATGTTTGGA TATTCTTGGT CTGGTTTCCA GT - #TTGAGATG       60     - GGACTGCCAG GAAGTGAAGT GGAAAGCGAC TGGTGGGTGT GGGTTCACGA CA - #AGGAGAAC      120     - ATAGCATCAG GTCTAGTAAG TGGAGATCTA CCAGAGAACG GCCCAGCATA TT - #GGCACCTC      180     - TATAAGCAAG ATCATGACAT TGCAGAAAAG CTAGGAATGG ATTGTATTAG AG - #GTGGCATT      240     - GAGTGGGCAA GAATTTTTCC AAAGCCAACA TTTGACGTTA AAGTTGATGT GG - #AAAAGGAT      300     - GAAGAAGGCA ACATAATTTC CGTAGACGTT CCAGAGAGTA CAATAAAAGA GC - #TAGAGAAA      360     - ATTGCCAACA TGGAGGCCCT TGAACATTAT CGCAAGATTT ACTCAGACTG GA - #AGGAGAGG      420     - GGCAAAACCT TCATATTAAA CCTCTACCAC TGGCCTCTTC CATTATGGAT TC - #ATGACCCA      480     - ATTGCAGTAA GGAAACTTGG CCCGGATAGG GCTCCTGCAG GATGGTTAGA TG - #AGAAGACA      540     - GTGGTAGAGT TTGTGAAGTT TGCCGCCTTC GTTGCTTATC ACCTTGATGA CC - #TCGTTGAC      600     - ATGTGGAGCA CAATGAACGA ACCAAACGTA GTCTACAATC AAGGTTACAT TA - #ATCTACGT      660     - TCAGGATTTC CACCAGGATA TCTAAGCTTT GAAGCAGCAG AAAAGGCAAA AT - #TCAACTTA      720     - ATTCAGGCTC ACATCGGAGC ATATGATGCC ATAAAAGAGT ATTCAGAAAA AT - #CCGTGGGA      780     - GTGATATACG CCTTTGCTTG GCACGATCCT CTAGCGGAGG AGTATAAGGA TG - #AAGTAGAG      840     - GAAATCAGAA AGAAAGACTA TGAGTTTGTA ACAATTCTAC ACTCAAAAGG AA - #AGCTAGAC      900     - TGGATCGGCG TAAACTACTA CTCCAGGCTG GTATATGGAG CCAAAGATGG AC - #ACCTAGTT      960     - CCTTTACCTG GATATGGATT TATGAGTGAG AGAGGAGGAT TTGCAAAGTC AG - #GAAGACCT     1020     - GCTAGTGACT TTGGATGGGA AATGTACCCA GAGGGCCTTG AGAACCTTCT TA - #AGTATTTA     1080     - AACAATGCCT ACGAGCTACC AATGATAATT ACAGAGAACG GTATGGCCGA TG - #CAGCAGAT     1140     - AGATACAGGC CACACTATCT CGTAAGCCAT CTAAAGGCAG TTTACAATGC TA - #TGAAAGAA     1200     - GGTGCTGATG TTAGAGGGTA TCTCCACTGG TCTCTAACAG ACAACTACGA AT - #GGGCCCAA     1260     - GGGTTCAGGA TGAGATTTGG ATTGGTTTAC GTGGATTTCG AGACAAAGAA GA - #GATATTTA     1320     - AGGCCAAGCG CCCTGGTATT CAGAGAAATA GCCACTCAAA AAGAAATTCC AG - #AAGAATTA     1380     - GCTCACCTCG CAGACCTCAA ATTTGTTACC AAGAAAGTAG CCATTTCATT TT - #TTCTTTGT     1440     #     1476         TTGG GAAAATAAGA TCATAA     - (2) INFORMATION FOR SEQ ID NO:5:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  491 ami - #no acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:5: (xi) SEQUENCE DESCRIPTION: SEQ     -      Met Leu Ser Phe Pro Lys Gly Phe - # Lys Phe Gly Trp Ser Gln Ser     #    15     -      Gly Phe Gln Ser Glu Met Gly Thr - # Pro Gly Ser Glu Asp Pro Asn     #    30     -      Ser Asp Trp His Val Trp Val His - # Asp Arg Glu Asn Ile Val Ser     #    45     -      Gln Val Val Ser Gly Asp Leu Pro - # Glu Asn Gly Pro Gly Tyr Trp     #    60     -      Gly Asn Tyr Lys Arg Phe His Asp - # Glu Ala Glu Lys Ile Gly Leu     #    75     -      Asn Ala Val Arg Ile Asn Val Glu - # Trp Ser Arg Ile Phe Pro Arg     #    90     -      Pro Leu Pro Lys Pro Glu Met Gln - # Thr Gly Thr Asp Lys Glu Asn     #   105     -      Ser Pro Val Ile Ser Val Asp Leu - # Asn Glu Ser Lys Leu Arg Glu     #   120     -      Met Asp Asn Tyr Ala Asn His Glu - # Ala Leu Ser His Tyr Arg His     #   135     -      Ile Leu Glu Asp Leu Arg Asn Arg - # Gly Phe His Ile Val Leu Asn     #   150     -      Met Tyr His Trp Thr Leu Pro Ile - # Trp Leu His Asp Pro Ile Arg     #   165     -      Val Arg Arg Gly Asp Phe Thr Gly - # Pro Thr Gly Trp Leu Asn Ser     #   180     -      Arg Thr Val Tyr Glu Phe Ala Arg - # Phe Ser Ala Tyr Val Ala Trp     #   195     -      Lys Leu Asp Asp Leu Ala Ser Glu - # Tyr Ala Thr Met Asn Glu Pro     #   210     -      Asn Val Val Trp Gly Ala Gly Tyr - # Ala Phe Pro Arg Ala Gly Phe     #   225     -      Pro Pro Asn Tyr Leu Ser Phe Arg - # Leu Ser Glu Ile Ala Lys Trp     #   240     -      Asn Ile Ile Gln Ala His Ala Arg - # Ala Tyr Asp Ala Ile Lys Ser     #   255     -      Val Ser Lys Lys Ser Val Gly Ile - # Ile Tyr Ala Asn Thr Ser Tyr     #   270     -      Tyr Pro Leu Arg Pro Gln Asp Asn - # Glu Ala Val Glu Ile Ala Glu     #   285     -      Arg Leu Asn Arg Trp Ser Phe Phe - # Asp Ser Ile Ile Lys Gly Glu     #   300     -      Ile Thr Ser Glu Gly Gln Asn Val - # Arg Glu Asp Leu Arg Asn Arg     #   315     -      Leu Asp Trp Ile Gly Val Asn Tyr - # Tyr Thr Arg Thr Val Val Thr     #   330     -      Lys Ala Glu Ser Gly Tyr Leu Thr - # Leu Pro Gly Tyr Gly Asp Arg     #   345     -      Cys Glu Arg Asn Ser Leu Ser Leu - # Ala Asn Leu Pro Thr Ser Asp     #   360     -      Phe Gly Trp Glu Phe Phe Pro Glu - # Gly Leu Tyr Asp Val Leu Leu     #   375     -      Lys Tyr Trp Asn Arg Tyr Gly Leu - # Pro Leu Tyr Val Met Glu Asn     #   390     -      Gly Ile Ala Asp Asp Ala Asp Tyr - # Gln Arg Pro Tyr Tyr Leu Val     #   405     -      Ser His Ile Tyr Gln Val His Arg - # Ala Leu Asn Glu Gly Val Asp     #   420     -      Val Arg Gly Tyr Leu His Trp Ser - # Leu Ala Asp Asn Tyr Glu Trp     #   435     -      Ser Ser Gly Phe Ser Met Arg Phe - # Gly Leu Leu Lys Val Asp Tyr     #   450     -      Leu Thr Lys Arg Leu Tyr Trp Arg - # Pro Ser Ala Leu Val Tyr Arg     #   465     -      Glu Ile Thr Arg Ser Asn Gly Ile - # Pro Glu Glu Leu Glu His Leu     #   480     -      Asn Arg Val Pro Pro Ile Lys Pro - # Leu Arg His     #   490     - (2) INFORMATION FOR SEQ ID NO:6:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  489 ami - #no acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:6: (xi) SEQUENCE DESCRIPTION: SEQ     -      Met Tyr Ser Phe Pro Asn Ser Phe - # Arg Phe Gly Trp Ser Gln Ala     #    15     -      Gly Phe Gln Ser Glu Met Gly Thr - # Pro Gly Ser Glu Asp Pro Asn     #    30     -      Thr Asp Trp Tyr Lys Trp Val His - # Asp Pro Glu Asn Met Ala Ala     #    45     -      Gly Leu Val Ser Gly Asp Leu Pro - # Glu Asn Gly Pro Gly Tyr Trp     #    60     -      Gly Asn Tyr Lys Thr Phe His Asp - # Asn Ala Gln Lys Met Gly Leu     #    75     -      Lys Ile Ala Arg Leu Asn Val Glu - # Trp Ser Arg Ile Phe Pro Asn     #    90     -      Pro Leu Pro Arg Pro Gln Asn Phe - # Asp Glu Ser Lys Gln Asp Val     #   105     -      Thr Glu Val Glu Ile Asn Glu Asn - # Glu Leu Lys Arg Leu Asp Glu     #   120     -      Tyr Ala Asn Lys Asp Ala Leu Asn - # His Tyr Arg Glu Ile Phe Lys     #   135     -      Asp Leu Lys Ser Arg Gly Leu Tyr - # Phe Ile Leu Asn Met Tyr His     #   150     -      Trp Pro Leu Pro Leu Trp Leu His - # Asp Pro Ile Arg Val Arg Arg     #   165     -      Gly Asp Phe Thr Gly Pro Ser Gly - # Trp Leu Ser Thr Arg Thr Val     #   180     -      Tyr Glu Phe Ala Arg Phe Ser Ala - # Tyr Ile Ala Trp Lys Phe Asp     #   195     -      Asp Leu Val Asp Glu Tyr Ser Thr - # Met Asn Glu Pro Asn Val Val     #   210     -      Gly Gly Leu Gly Tyr Val Gly Val - # Lys Ser Gly Phe Pro Pro Gly     #   225     -      Tyr Leu Ser Phe Glu Leu Ser Arg - # Arg His Met Tyr Asn Ile Ile     #   240     -      Gln Ala His Ala Arg Ala Tyr Asp - # Gly Ile Lys Ser Val Ser Lys     #   255     -      Lys Pro Val Gly Ile Ile Tyr Ala - # Asn Ser Ser Phe Gln Pro Leu     #   270     -      Thr Asp Lys Asp Met Glu Ala Val - # Glu Met Ala Glu Asn Asp Asn     #   285     -      Arg Trp Trp Phe Phe Asp Ala Ile - # Ile Arg Gly Glu Ile Thr Arg     #   300     -      Gly Asn Glu Lys Ile Val Arg Asp - # Asp Leu Lys Gly Arg Leu Asp     #   315     -      Trp Ile Gly Val Asn Tyr Tyr Thr - # Arg Thr Val Val Lys Arg Thr     #   330     -      Glu Lys Gly Tyr Val Ser Leu Gly - # Gly Tyr Gly His Gly Cys Glu     #   345     -      Arg Asn Ser Val Ser Leu Ala Gly - # Leu Pro Thr Ser Asp Phe Gly     #   360     -      Trp Glu Phe Phe Pro Glu Gly Leu - # Tyr Asp Val Leu Thr Lys Tyr     #   375     -      Trp Asn Arg Tyr His Leu Tyr Met - # Tyr Val Thr Glu Asn Gly Ile     #   390     -      Ala Asp Asp Ala Asp Tyr Gln Arg - # Pro Tyr Tyr Leu Val Ser His     #   405     -      Val Tyr Gln Val His Arg Ala Ile - # Asn Ser Gly Ala Asp Val Arg     #   420     -      Gly Tyr Leu His Trp Ser Leu Ala - # Asp Asn Tyr Glu Trp Ala Ser     #   435     -      Gly Phe Ser Met Arg Phe Gly Leu - # Leu Lys Val Asp Tyr Asn Thr     #   450     -      Lys Arg Leu Tyr Trp Arg Pro Ser - # Ala Leu Val Tyr Arg Glu Ile     #   465     -      Ala Thr Asn Gly Ala Ile Thr Asp - # Glu Ile Glu His Leu Asn Ser     #   480     -      Val Pro Pro Val Lys Pro Leu Arg - # His     #   485     - (2) INFORMATION FOR SEQ ID NO:7:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  12 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:7: (xi) SEQUENCE DESCRIPTION: SEQ     -      Asp Trp Ile Gly Val Asn Tyr Tyr - # Ser Arg Leu Val     #    10     - (2) INFORMATION FOR SEQ ID NO:8:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  13 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:8: (xi) SEQUENCE DESCRIPTION: SEQ     -      Pro Ala Ser Asp Phe Gly Trp Glu - # Met Tyr Pro Glu Gly     #    10     - (2) INFORMATION FOR SEQ ID NO:9:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  23 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:9: (xi) SEQUENCE DESCRIPTION: SEQ     -      Gly Tyr Leu His Trp Ser Leu Thr - # Asp Asn Tyr Glu Trp Ala Gln     #    15     -      Gly Phe Arg Met Arg Phe Gly Leu     #    20     - (2) INFORMATION FOR SEQ ID NO:10:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  7 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 4 can be Phe or Ser     #ID NO:10:(xi) SEQUENCE DESCRIPTION: SEQ     -      Gly Phe Gln Xaa Glu Met Gly     #    5 1     - (2) INFORMATION FOR SEQ ID NO:11:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 8 can be Glu or Asn     #ID NO:11:(xi) SEQUENCE DESCRIPTION: SEQ     -      Val Ser Gly Asp Leu Pro Glu Xaa - # Gly     #    5 1     - (2) INFORMATION FOR SEQ ID NO:12:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 3 can be Ser or Ala;     #position 8 can be Trp, Lys, Arg or Asn     #ID NO:12:(xi) SEQUENCE DESCRIPTION: SEQ     -      Glu Trp Xaa Arg Ile Phe Pro Xaa - # Pro     #    5 1     - (2) INFORMATION FOR SEQ ID NO:13:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 3 can be Tyr, Leu or     #at position 5 can be Leu or Ile     #ID NO:13:(xi) SEQUENCE DESCRIPTION: SEQ     -      Leu Pro Xaa Trp Xaa His Asp Pro - # Ile     #    5 1     - (2) INFORMATION FOR SEQ ID NO:14:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  13 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 2 can be Phe or Met;     #position 6 can be Met or Asn; Xaa at positio - #n 9     #Val, Tyr, Trp or Gly; Xaa at position 10 can - # be     #or Gly; Xaa at position 11 can be Leu, Gln                    Ala     #ID NO:14:(xi) SEQUENCE DESCRIPTION: SEQ     -      Thr Xaa Asn Glu Pro Xaa Val Val - # Xaa Xaa Xaa Gly Tyr     #    10     - (2) INFORMATION FOR SEQ ID NO:15:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  12 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 2 can be Asn or Gln;     #position 5 can be Ala or Ile; Xaa at positio - #n 6     #Arg orly or Arg; Xaa at position 9 can be     #at position 10 can be Gln, Ala or Gly     #ID NO:15:(xi) SEQUENCE DESCRIPTION: SEQ     -      Ile Xaa Ala His Xaa Xaa Ala Tyr - # Xaa Xaa Ile Lys     #    10     - (2) INFORMATION FOR SEQ ID NO:16:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  12 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 9 can be Thr or Ser;     #position 11 can be Glu, Leu or Thr     #ID NO:16:(xi) SEQUENCE DESCRIPTION: SEQ     -      Asp Trp Ile Gly Val Asn Tyr Tyr - # Xaa Arg Xaa Val     #    10     - (2) INFORMATION FOR SEQ ID NO:17:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  13 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 2 can be Val, Ala or     #at position 5 can be Ile or Phe; Xaa at p - #osition     #be Tyr, Met or Phe; Xaa at position 10 can                    or Phe     #ID NO:17:(xi) SEQUENCE DESCRIPTION: SEQ     -      Pro Xaa Ser Asp Xaa Gly Trp Glu - # Xaa Xaa Pro Glu Gly     #    10     - (2) INFORMATION FOR SEQ ID NO:18:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  11 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 2 can be Ile, Arg or     #at position 3 can be Leu, Tyr or Gln; Xaa     #6 can be Tyr or His; Xaa at position 8 ca - #n be     #Leu; Xaa at position 9 can be Ala or Val     #ID NO:18:(xi) SEQUENCE DESCRIPTION: SEQ     -      Asp Xaa Xaa Arg Pro Xaa Tyr Xaa - # Xaa Ser His     #    10     - (2) INFORMATION FOR SEQ ID NO:19:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  23 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     -     (ix) FEATURE:     # Xaa at position 3 can be Phe or Leu;     #position 6 can be Ala or Ser; Xaa at positio - #n 8     #or Tyr Ala; Xaa at position 11 can be Phe     #positionion 14 can be Ala or Ser; Xaa at     #be Arg, Gln or Ser; Xaa at position 18 can                    or Ser     #ID NO:19:(xi) SEQUENCE DESCRIPTION: SEQ     -      Gly Tyr Xaa His Trp Xaa Leu Xaa - # Asp Asn Xaa Glu Trp Xaa Xaa     Gly Phe     #    15     -      Xaa Met Arg Phe Gly Leu                   20     - (2) INFORMATION FOR SEQ ID NO:20:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  7 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:20:(xi) SEQUENCE DESCRIPTION: SEQ     -      Gly Phe Gln Phe Glu Met Gly     #    5 1     - (2) INFORMATION FOR SEQ ID NO:21:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:21:(xi) SEQUENCE DESCRIPTION: SEQ     -      Val Ser Gly Asp Leu Pro Glu Glu - # Gly     #    5 1     - (2) INFORMATION FOR SEQ ID NO:22:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:22:(xi) SEQUENCE DESCRIPTION: SEQ     -      Glu Trp Ser Arg Ile Phe Pro Trp - # Pro     #    5 1     - (2) INFORMATION FOR SEQ ID NO:23:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:23:(xi) SEQUENCE DESCRIPTION: SEQ     -      Leu Pro Tyr Trp Leu His Asp Pro - # Ile     #    5 1     - (2) INFORMATION FOR SEQ ID NO:24:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  13 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:24:(xi) SEQUENCE DESCRIPTION: SEQ     -      Thr Phe Asn Glu Pro Met Val Val - # Val Glu Leu Gly Tyr     #    10     - (2) INFORMATION FOR SEQ ID NO:25:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  12 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:25:(xi) SEQUENCE DESCRIPTION: SEQ     -      Ile Asn Ala His Ala Leu Ala Tyr - # Arg Gln Ile Lys     #    10     - (2) INFORMATION FOR SEQ ID NO:26:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  12 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:26:(xi) SEQUENCE DESCRIPTION: SEQ     -      Asp Trp Ile Gly Val Asn Tyr Tyr - # Thr Arg Glu Val     #    10     - (2) INFORMATION FOR SEQ ID NO:27:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  13 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:27:(xi) SEQUENCE DESCRIPTION: SEQ     -      Pro Val Ser Asp Ile Gly Trp Glu - # Leu Tyr Pro Glu Gly     #    10     - (2) INFORMATION FOR SEQ ID NO:28:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  11 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:28:(xi) SEQUENCE DESCRIPTION: SEQ     -      Asp Ile Leu Arg Pro Tyr Tyr Ile - # Ala Ser His     #    10     - (2) INFORMATION FOR SEQ ID NO:29:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  23 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:29:(xi) SEQUENCE DESCRIPTION: SEQ     -      Gly Tyr Phe His Trp Ala Leu Thr - # Asp Asn Phe Glu Trp Ala Leu     Gly Phe     #    15     -      Arg Met Arg Phe Gly Leu                   20     - (2) INFORMATION FOR SEQ ID NO:30:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:30:(xi) SEQUENCE DESCRIPTION: SEQ     -      Glu Trp Ala Arg Ile Phe Pro Lys - # Pro     #    5 1     - (2) INFORMATION FOR SEQ ID NO:31:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  9 amino - # acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:31:(xi) SEQUENCE DESCRIPTION: SEQ     -      Leu Pro Leu Trp Ile His Asp Pro - # Ile     #    5 1     - (2) INFORMATION FOR SEQ ID NO:32:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  13 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:32:(xi) SEQUENCE DESCRIPTION: SEQ     -      Thr Met Asn Glu Pro Asn Val Val - # Tyr Asn Gln Gly Tyr     #    10     - (2) INFORMATION FOR SEQ ID NO:33:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  12 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:33:(xi) SEQUENCE DESCRIPTION: SEQ     -      Ile Gln Ala His Ile Gly Ala Tyr - # Asp Ala Ile Lys     #    10     - (2) INFORMATION FOR SEQ ID NO:34:     -      (i) SEQUENCE CHARACTERISTICS:               (A) LENGTH:  11 amin - #o acid residues               (B) TYPE:  amino aci - #d               (C) STRANDEDNESS:  sing - #le               (D) TOPOLOGY:  linear     -     (ii) MOLECULE TYPE: peptide     #ID NO:34:(xi) SEQUENCE DESCRIPTION: SEQ     -      Asp Arg Tyr Arg Pro His Tyr Leu - # Val Ser His     #    10     __________________________________________________________________________ 

What we claim is:
 1. An isolated DNA encoding a polypeptide possessing β-galactosidase activity of about 80% or above after being subjected to heat treatment at 90° C. for 120 minutes, and having a DNA sequence which hybridizes with a DNA sequence complementary to the DNA sequence shown in SEQ ID NO. 2 under stringent conditions.
 2. An isolated DNA encoding a polypeptide possessing SDS-resistant β-galactosidase activity of about 80% or above after being subjected to heat treatment at 90° C. for 120 minutes in the presence of 1% SDS, and having a DNA sequence which hybridizes with a DNA sequence complementary to the DNA sequence shown in SEQ ID NO. 4 under stringent conditions.
 3. A method of cloning a DNA having a sequence encoding a polypeptide possessing SDS-resistant β-galactosidase activity of about 80% or above after being subjected to heat treatment at 90° C. for 120 minutes in the presence of 1% SDS, which comprises:isolating a gene which hybridizes under stringent conditions with a probe, said probe selected from the group consisting of:(a) a DNA having the DNA sequences shown in SEQ ID No. 4, (b) a DNA encoding the amino acid sequence shown in SEQ ID No. 3, (c) a DNA fragment of SEQ ID NO. 2 or 4, which encodes the amino acid sequence shown in SEQ ID No. 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19, and (d) a DNA produced by PCR amplification of a gene library of a hyperthermophilic bacteria using PCR primers selected from the group consisting of DNA fragments encoding the amino acid sequence shown in SEQ ID No. 7, 8, 9, 2, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 or 34, ligating said gene to an expression vector and introducing said vector into a host cell, and measuring the β-galactosidase activity of said transformed host cell.
 4. The method of cloning a DNA according to claim 3, wherein the probe is the DNA having the DNA sequence shown in SEQ ID No.
 4. 5. The method of cloning a DNA according to claim 3, wherein the probe is the DNA encoding the amino acid sequence shown in SEQ ID No.
 3. 6. The method of cloning a DNA according to claim 3, wherein the probe is the DNA fragment of SEQ ID NO. 2 or 4, which encodes the amino acid sequence shown in SEQ ID No. 10, 11, 12, 13, 14, 15, 16, 17, 18 or
 19. 7. The method of cloning a DNA according to claim 3, wherein the probe is the DNA produced by PCR amplification of a gene library of a hyperthermophilic bacteria using PCR primers selected from the group consisting of DNA fragments encoding the amino acid sequence shown in SEQ ID No. 7, 8, 9, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 or
 34. 